UNIVERSITY   OF  CALIFORNIA 

CTURAL    DEPARTMENT  LIBRARY 


GIFT   OF 
.'Irs.    Lycila   Bart)' 


CEMENT  AND  CONCRETE 


BY 


LOUIS   CAELTON   SABIN,  B.  S.,  C.  E. 

ASSISTANT  ENGINEER,  ENGINEER  DEPARTMENT,  U.  S.  ARMY;   MEMBER  OF  THE 
AMERICAN  SOCIETY  OF  CIVIL  ENGINEERS 


NEW  YORK 

McGRAW    PUBLISHING    COMPANY 

1905 


S'a- 


COPYBIGHT,  1904 
BY 

L.   C.  SABIN 


Stanbope 


BOSTON,      U.S.A. 


PREFACE 


THAT  the  use  of  cement  has  outstripped  the  literature  on 
the  subject  is  evidenced  by  the  number  and  character  of  the 
inquiries  addressed  to  technical  journals  concerning  it.  This 
volume  is  not  designed  to  fill  the  proverbial  "long  felt  want/' 
for  until  within  a  few  years  the  number  of  engineers  using 
cement  in  large  quantities  was  quite  limited.  These  American 
pioneers  in  cement  engineering,  under  one  of  whom  the  author 
received  his  first  practical  training  in  this  line,  needed  no  formal 
introduction  to  the  use  and  properties  of  cement;  their  knowl- 
edge was  born  and  nurtured  through  intimate  association  and 
careful  observation. 

To-day  the  young  engineer  frequently  finds  a  good  working 
knowledge  of  cement  one  of  the  essentials  of  success,  and  the 
gaining  of  this  knowledge  by  experience  alone  is  likely  to  be 
too  slow  and  expensive,  judged  by  twentieth  century  standards. 
In  fact,  the  variety  and  extent  of  the  uses  to  which  cement  is 
applied,  and  the  knowledge  concerning  its  properties,  have  of 
late  increased  so  rapidly  that  even  the  older  engineer,  whose 
practice  may  have  directed  his  special  attention '  along  other 
channels  for  a  few  years,  finds  it  difficult  to  follow  its  progress. 

One  who  wishes  only  a  catechetical  reply  to  any  question 
that  may  arise  concerning  cement  and  its  use  will  be  somewhat 
disappointed  in  these  pages;  on  the  other  hand,  he  who  would 
devote  special  attention  to  the  subject  must,  of  course,  go  far 
beyond  them.  The  author  has  attempted  to  take  a  middle 
course,  avoiding  on  the  one  hand  a  dogmatic  statement  of  facts, 
and  on  the  other  too  detailed  and  extended  series  of  tests,  but 
giving,  where  practicable,  sufficient  tests  to  support  the  state- 
ments made,  and  endeavoring  to  show  the  connection  between 
theory  and  practice,  the  laboratory  and  the  field. 

The  original  investigations  forming  the  basis  of  the  work 
were  made  in  connection  with  the  construction  of  the  Poe 
Lock  at  St.  Marys  Falls  Canal,  Michigan,  under  the  direction 

iii 


iv  PREFACE 

of  the  Corps  of  Engineers,  U.  S.  Army.  To  the  late  General 
O.  M.  Poe,  the  Engineer  officer  in  charge  of  the  district  at  that 
time,  and  to  Mr.  E.  S.  Wheeler,  his  chief  assistant  engineer, 
m&y  be  credited  a  very  large  share  of  the  value  of  the  results 
obtained,  since  the  accomplishment  of  a  series  of  experiments 
of  so  comprehensive  a  character  was  made  possible  only  through 
the  broad  views  held  by  them  as  to  the  value  of  thorough  tests 
of  cement. 

The  author  wishes  to  express  his  appreciation  of  the  courtesy 
of  General  G.  L.  Gillespie,  Chief  of  Engineers,  U.  S.  A.,  in  grant- 
ing permission  to  use  the  data  collected,  and  of  the  kindness 
of  Major  W.  H.  Bixby  in  presenting  a  request  for  this  per- 
mission. 

When  not  otherwise  stated,  the  tables  in  the  work  are  con- 
densed from  the  results  of  the  above  mentioned  investigations. 
In  supplementing  this  original  matter,  much  use  has  been  made 
of  the  experiments  of  others  as  published  in  society  transac- 
tions, technical  journals,  etc.,  to  all  of  whom  credit  has  been 
given  in  the  body  of  the  work. 

If  this  attempt  to  place  in  one  volume  a  connected  story  of 
the  properties  and  use  of  cement  serves  to  make  the  road  to 
this  knowledge  a  little  less  devious  than  that  followed  by  the 
writer,  the  latter  will  be  rewarded. 

L.  C.  S. 

SAULT  STE.  MARIE,  MICH. 
January  3,  1905. 


CONTENTS 


PART  I.     CEMENT:  CLASSIFICATION   AND 
MANUFACTURE 

CHAFFER   I.     DEFINITIONS  AND   CONSTITUENTS 

PAfiK 

ART.  1.  GENERAL  CLASSIFICATION  OF  HYDRAULIC  PRODUCTS  ....  1 

ART.  2.  LIME:  COMMON  AND  HYDRAULIC      3 

ART.  3.  PORTLAND  CEMENT 4 

ART.  4.  SLAG  CEMENT 7 

ART.  5.  NATURAL  CEMENT 8 

CHAPTER  II.     MANUFACTURE 

ART.  6.     MANUFACTURE  OF  PORTLAND  CEMENT 10 

Materials.  —  Wet  Process.  —  Dry  Process.  —  Semi-dry  Process.  — 
Details  of  the  Manufacture:  Burning,  Grinding.  — Sand-Cement. 

ART.  7.     OTHER  METHODS  OF  MANUFACTURE  OF  PORTLAND     ....  22 

ART.  8.     MANUFACTURE  OF  SLAG  CEMENT 23 

ART.  9.     MANUFACTURE  OF  NATURAL  CEMENT  24 


PART  II.  PROPERTIES  OF  CEMENT  AND 
METHODS  OF  TESTING 

CHAFfER   III.     INTRODUCTORY 
Desirable  Qualities.  —  Uniform  Methods  of  Testing 28 

CHAPTER  IV.     CHEMICAL  TESTS 
ART.  10.     COMPOSITION  AJMD  CHEMICAL  ANALYSIS 31 

CHAPTER  V.     THE  SIMPLER   PHYSICAL  TESTS 

ART.  11.     MICROSCOPICAL  TESTS. — COLOR 36 

ART.  12.     WEIGHT  PER  CUBIC  FOOT,  OR  APPARENT  DENSITY  ....       37 
ART.  13.     SPECIFIC  GRAVITY,  OR  TRUE  DENSITY.   .  • 39 

CHAPTER  VI.     SIFTING  AND   FINE  GRINDING 

ART.  14.     FINENESS 45 

Importance  of  Fineness.  —  Sieves.  —  Methods.  —  Specifications. 


v 


vi  CONTENTS 

PAGE 
ART.  15.     COARSE  PARTICLES  IN  CEMENT 52 

Effect  on  Weight,  Time  of  Setting  and  Tensile  Strength. 

ART.  16.     FINE  GRINDING 58 

Effect  on  Weight,  Time  of  Setting  and  Tensile  Strength. 

CHAPTER   VII.     TIMfe   OF  SETTING   AND   SOUNDNESS 

ART.  17.     SETTING  OF  CEMENT 65 

Process  of  Setting.  —  Rate.  —  Variations  in  Rate. 
ART.  18.     CONSTANCY  OF  VOLUME 76 

Causes  of  Unsoundness.  —  Tests.  —  Discussion  of  Methods.  —  Hot 

Tests  for  Natural  Cements.  —  Conclusions. 

CHAPTER   VIII.     TESTS   OF   THE   STRENGTH   OF  CEMENT 
IN  COMPRESSION,   ADHESION,   ETC. 

ART.  19.     TESTS  IN  COMPRESSION  AND  SHEAR 89 

ART.  20.     TESTS  OF  TRANSVERSE  STRENGTH 90 

ART.  21.     TESTS  OF  ADHESION  AND  ABRASION 92 

CHAPTER   IX.     TENSILE   TESTS   OF  COHESION 

ART.  22.     SAND  FOR  TESTS 95 

Value  of  Tests  of  Sand  Mortars.  —  Uniformity  in  Sand.  —  Com- 
parison of  Different  Kinds.  —  Tests  with  Natural  Sand.  —  Fineness. 

ART.  23.     MAKING  BRIQUETS 97 

Proportions.  —  Consistency.  —  Temperature.  —  Gaging:  Hand  and 
Machine.  —  Methods.  —  Amount  of  Gaging.  —  Form  of  Briquets. 
—  Molds.  —  Molding.  —  Briquet  Machines.  —  Approved  Methods 
of  Hand  Molding.  —  Marking  the  Briquets. 

ART.  24.     STORING  BRIQUETS 117 

Time  in  Air  before  Immersion.  —  Moist  Closet.  —  Water  of  Im- 
mersion.—  Storing  in  Air;  in  Damp  Sand. 

ART.  25.     BREAKING  THE  BRIQUETS 

Testing  Machines.  —  Clips.  —  Clip-breaks.  —  Comparative  Tests  of     123 
Clips.  —  Requirements  for  a  Perfect  Clip.  —  Form  Recommended. 
—  Rate  of  Applying  Tensile  Stress.  —  Treatment  of  Results. 

ART.  26.     INTERPRETATION  OF  TENSILE  TESTS  OF  COHESION   ....     137 

CHAPTER  X.     RECEPTION  OF  CEMENT  AND  RECORDS 
OF  TESTS 

ART.  27.     STORING  AND  SAMPLING 144 

Storage  Houses.  —  Percentage  of  Barrels  to  Sample.  —  Method  of 

Taking  and  Storing  the  Sample. 
ART.  28.     RECORDS  OF  TESTS 146 

Value  of  Records.  —  Marking  Specimens.  —  Records  at  St.  Marys 

Falls  Canal. 


CONTENTS  vii 

PART   III.     THE   PREPARATION   AND   PROP- 
ERTIES  OF   MORTAR   AND   CONCRETE 

CHAPTER  XI.     SAND   FOR   MORTAR 

PAGK 

ART.  29.     CHARACTER  OF  THE  SAND 154 

Shape  and  Hardness  of  the  Grains.  —  Siliceous  vs.  Calcareous 
Sands.  —  Slag  Sand.  —  Sand  for  Use  in  Sea  Water. 

ART.  30.     FINENESS  OF  SAND 150 

Relation  Volume  and  Superficial  Area.  —  Effect  of  Fineness. 

ART.  31.     VOIDS  IN  SAND 162 

Conditions  Affecting  Voids:  Shape  of  Grains;  Granulometric  Com- 
position. —  Effect  on  Tensile  Strength  of  Mortar.  —  Moist  Sand. 

ART.  32.     IMPURITIES  IN  SAND 168 

ART.  33.     CONCLUSIONS. — WEIGHT  AND  COST  OF  SAND 170 

CHAPTER   XII.     MORTAR:   MAKING   AND   COST 

ART.  34.     PROPORTIONS  OF  THE  INGREDIENTS 172 

Capacity  of  Cement  Barrels.  —  Equivalent  Proportions  by  Weight 
and  Volume.  —  Richness  of  Mortars.  —  Effect  of  Pebbles.  —  Con- 
sistency. 

ART.  35.     MIXING  THE  MORTAR 177 

Hand  Mixing.  —  Machine  Mixing. 

ART.  36.     COST  OF  MORTARS 179 

Ingredients  Required.  —  Tables  of  Quantities.  —  Estimates  of 
Cost.  —  Tables  of  Cost  of  Portland  and  Natural  Cement  Mortars. 

CHAPTER  XIII.     CONCRETE:   AGGREGATES 

ART.  37.     CHARACTER  OF  AGGREGATES 186 

Proper  Materials.  —  Screenings  in  Broken  Stone.  —  Foreign  In- 
gredients. 

ART.  38.     SIZE  AND  SHAPE  OF  FRAGMENTS  AND  VOLUME  OF  VOIDS  .    .     188 
Conditions  Affecting  Voids.  —  Effect  on  Strength  oT  Concrete.  — 
Gravel  vs.  Broken  Stone. 

ART.  39.     STONE  CRUSHING  AND  COST  OF  AGGREGATE 194 

Breaking  Stone  by  Hand.  —  Stone  Crushers.  —  Cost  of  Aggregate. 
—  Examples. 

.CHAPTER  XIV.     CONCRETE   MAKING:   METHODS 
AND    COST 

ART.  40.     PROPORTIONS  OF  THE  INGREDIENTS 200 

Theory  of  Proportions.  —  Determination  of  Amount  of  Mortar 
Required.  —  Aggregates  Containing  Sand.  —  Required  Strength. 

ART.  41.     MIXING  CONCRETE  BY  HAND      203 

Hand  vs.  Machine  Mixing.  —  Method  of  Hand  Mixing;  Number  of 
Men  and  Output;  Examples. 


viii  CONTENTS 

PAGE 
ART.  42.     CONCRETE  MIXING  MACHINES 207 

General     Classification.  —  Description     of     Machines.  —  Basis    of 

Comparison. 

ART.  43.     CONCRETE  MIXING  PLANTS  AND  COST  OF  MACHINE  MIXING     212 
ART.  44.     COST  OF  CONCRETE 218 

Ingredients  Required  for  a  Cubic  Yard.  —  Examples  of  Actual  Cost. 

CHAPTER  XV.     THE  TENSILE  AND  ADHESIVE  STRENGTH 
OF  CEMENT  MORTARS  AND  THE  EFFECT  OF  VARIATIONS 

IN  TREATMENT 
ART.  45.     TENSILE  STRENGTH  OF  MORTARS  OF  VARIOUS  COMPOSITIONS  . 

AND  AGES 227 

ART.  46.     CONSISTENCY  OF  MORTAR  AND  AERATION  OF  CEMENT      .    .     232 

ART.  47.     REGAGING  OF  CEMENT  MORTAR 236 

ART.  48.     MIXTURES  OF  CEMENT  WITH  LIME,  PLASTER  PARIS,  ETC.  .     243 

Mixtures    of    Portland    and    Natural.  —  "Improved"    Cement.— 

Ground  Quicklime  with  Cement;  Slaked  Lime;  Plaster  of  Paris.  — 

Conclusions. 
ART.  49.     MIXTURES  OF  CLAY  AND  OTHER  MATERIALS  WITH  CEMENT.     253 

Effect  of  Powdered  Limestone,  Brick,  etc. ;  Sawdust ;  Terra  Cotta. 
ART.  50.     USE  OF  CEMENT  MORTARS  IN  FREEZING  WEATHER      .    .    .     260 

Effect  of  Frost  on  Set  Mortars.  —  Effect  of  Salt;  Heating  Materials; 

Consistency ;  Fineness  of  Sand.  —  Conclusions. 
ART.  51.     THE  ADHESION  OF  CEMENT 270 

Adhesion  between  Portland  and  Natural.  —  Adhesion  to  Stone  and 

Other  Materials.  — Effect  of  Consistency;  Regaging;  Character  of 

Surface  of  Stone.  —  Effect  of  Plaster  of  Paris.  —  Adhesion  to  Brick; 

Effect  of  Lime  Paste.  —  Adhesion  to  Rods  of  Iron  and  Steel. 

CHAPTER    XVI.     COMPRESSIVE    STRENGTH    AND  MOD- 
ULUS OF  ELASTICITY  OF  MORTAR  AND   CONCRETE 

ART.  52.     COMPRESSIVE  STRENGTH  OF  MORTARS 288 

Ratio  of  Compressive  to  Tensile  Strength. 
ART.  53.     CONCRETES  WITH  VARIOUS  PROPORTIONS  OF  INGREDIENTS     291 

Effect  of  Consistency;  Amount  and  Richness  of  Mortar;  Methods 

of  Storage. 
ART.  54.     CONCRETES  WITH  VARIOUS  KINDS  AND  SIZES  OF  AGGREGATES    298 

ART.  55.     CINDER  CONCRETE  AND  EFFECT  OF  CLAY 302 

ART.  56.     MODULUS  OF  ELASTICITY  OF  CEMENT  MORTAR  AND  CONCRETE     306 

CHAPTER    XVII.     THE    TRANSVERSE    STRENGTH    AND 
OTHER    PROPERTIES  OF  MORTAR  AND  CONCRETE 

ART.  57.     TRANSVERSE  STRENGTH 313 

Transverse  Strength  of  Mortars  Compared  to  Tensile  and  Com- 
pressive Strength.  —  Richness  of  Mortar;  Consistency.  —  Transverse 
Tests  of  Concrete  Bars:  Variations  in  Mortar  Used;  Consistency; 
Mixing ;  Aggregate ;  Screenings.  —  Deposition  in  Running  Water. 
—  Use  in  Freezing  Weather, 


CONTENTS  ix 

PAGE 

ART.  58.     RESISTANCE  TO  SHEAR  AND  ABRASION 328 

ART.  59.     EXPANSION  AND  CONTRACTION   OF    CEMENT  MORTAR,   AND 

THE  RESISTANCE  OF  CONCRETE  TO  FIRE 331 

Change  in  Volume  during  Setting.  —  Coefficient  of  Expansion  of 
Mortar  and  Concrete.  —  Fire-Resisting  Qualities  of  Concrete.  — 
Aggregate  for  Fireproof  Work. 

ART.  60.     PRESERVATION  OF  IRON  AND  STEEL  BY  MORTAR  AND  CONCRETE     336 
Action  of  Corrosion.  —  Tests  of  Effect  of  Concrete. 

ART.  61.     POROSITY,  PERMEABILITY,  ETC 340 

Porosity.  —  Permeability.  —  Waterproof  Mortars  and  Concretes.  — 
Washes  for  Exteriors  of  Walls.  —  Efflorescence.  —  Pointing  Mortar. 
—  Cements  in  Sea  Water. 


PART   IV.     USE   OF   MORTAR   AND   CONCRETE 

CHAPTER  XVIII.     CONCRETE:   DEPOSITION 

ART.  62.     TIMBER  FORMS  OR  MOLDS 351 

Sheathing.  —  Lining.  —  Posts  and  Braces. 

ART.  63.     DEPOSITION  OF  CONCRETE  IN  AIR 358 

Transporting,    Depositing,    Ramming.  —  Rubble   Concrete.  —  Fin- 
ish ;  Plastering;  Facing;  Bushhammering;  Colors  for  Concrete  Finish. 

ART.  64.     PLACING  CONCRETE  UNDER  WATER      369 

Laitance. — Tremie,    Skip,    etc. — Depositing    in    Bags;    Cost. — 
Block  System:  Molds;  Cost. 

CHAPTER  XIX.     CONCRETE-STEEL 

ART.  65.     MONIER  SYSTEM 381 

ART.  66.     WUNSCH,  MELAN,  AND  THACHER  SYSTEMS 383 

ART.  67.     OTHER  SYSTEMS  OF  CONCRETE-STEEL 385 

Hennebique,  Kahn,  Ransome,  Roeblirig,  Expanded  Metal. 

ART.  68.     THE  STRENGTH  OF  COMBINATIONS  OF  CONCRETE  AND  STEEL  387 

ART.  69.     BEAMS  WITH  SINGLE  REINFORCEMENT 390 

Formulas  for  Constant  Modulus  Elasticity;  for  Varying  Modulus. 

—  Excessive  Reinforcement.  —  Tables  of  Strength. 

ART.  70.     BEAMS  WITH  DOUBLE  REINFORCEMENT 403 

ART.  71.     SHEAR  IN  CONCRETE-STEEL  BEAMS 405 

CHAPTER  XX.     SPECIAL   USES  OF  CONCRETE:   BUILD- 
INGS, WALKS,   FLOORS,   AND   PAVEMENTS 

ART.  72.     BUILDINGS 410 

Roof;  Floor  System;  Columns.  — Building  Forms.  — N.  Y.  Build- 
ing Regulations. 

ART.  73.     WALKS 420 

Foundation;  Base;  Wearing  Surface;  Construction;  Cost. 

ART.  74.     FLOORS  OF  BASEMENTS,  STABLES,  AND  FACTORIES   ....     426 


x  CONTENTS 

PAGE 

ART.  75.     PAVEMENTS  AND  DRIVEWAYS      428 

Pavement  Foundations.  —  Concrete  Wearing  Surface.  —  Construc- 
tion. —  Example. 

ART.  76.     CURBS  AND  GUTTERS 431 

ART.  77.     STREET  RAILWAY  FOUNDATIONS 433 

CHAPTER  XXI.     SPECIAL  USES  OF  CONCRETE    (CONTINUED): 
SEWERS,   SUBWAYS,   AND   RESERVOIRS 

ART.  78.     SEWERS 436 

Methods  and  Cost.  —  Forms    . 
ART.  79.     SUBWAYS  AND  TUNNEL  LINING 443 

Waterproofing.  —  Subways.  —  Tunnels    in    Firm    Earth ;    in    Soft 
Ground;  in  Rock.  — Examples;  Methods;  Cost. 

ART.  80.     RESERVOIRS:  LININGS  AND  ROOFS 453 

Details  of  Construction.  — Groined  Arch.  — Forms.  — Examples; 
Cost. 

CHAPTER  XXII.     SPECIAL   USES  OF  CONCRETE    (CONTINUED): 
BRIDGES,    DAMS,   LOCKS,   AND    BREAKWATERS 

ART.  81.     BRIDGE  PIERS  AND  ABUTMENTS  AND  RETAINING  WALLS   .    .     464 

Bridge  Piers;  Steel  Shells.  —  Repair  of  Stone  Piers. — Retaining 

Walls  and  Abutments:  Coping;  Rules  for  Use  of  Concrete. 
ART.  82.     CONCRETE  PILES 471 

Building  in  Place.  — Concrete-Steel  Piles:  Molding;  Driving. 
ART.  83.     ARCHES 474 

Design;  Centers;  Construction;  Finish  and  Drainage.  —  Examples 

and  Cost. 
ART.  84.     DAMS 484 

Concrete   vs.    Rubble.  —  Quality   of   Concrete.  —  Construction.  — 

Examples. 
ART.  85.     LOCKS 488 

Methods  of  Building.  —  Examples. 
ART.  86.     BREAKWATERS    .  493 


PART  I 
CEMENT 

CLASSIFICATION  AND  MANUFACTURE 


CHAPTER  I 

DEFINITIONS   AND    CONSTITUENTS 
ART.   1.    GENERAL  CLASSIFICATION  OF  HYDRAULIC  PRODUCTS 

1.  The  use  of  a  cementitious  substance  for  binding  together 
fragments  of  stone  is  older  than  history,  and  it  is  known  that  the 
ancient  Romans  prepared  a  mortar  which  would  set  under 
water.  So  far  as  our  present  knowledge  of  cement  manufac- 
ture is  concerned,  however,  the  credit  of  demonstrating  that  a 
limestone  containing  clay  possessed,  when  burned  and  ground, 
the  property  of  hardening  under  water,  is  due  to  Mr.  John 
Smeaton,  who  announced  this  as  the  result  of  his  experiments 
made  in  1756  in  seeking  a  material  with  which  to  build  the 
Eddystone  Lighthouse.  After  this  discovery  by  Smeaton  nearly 
sixty  years  elapsed  before  M.  Vicat  gave  the  true  explanation 
of  this  action,  namely,  that  the  lime  during  burning  combined 
with  the  silica  to  form  silicate  of  lime,  the  essential  ingredient 
of  hydraulic  limes  and  cements. 

In  1796,  Parker,  of  London,  obtained  a  patent  for  the  manu- 
facture of  a  cement  from  septaria  nodules,  and  aptly  named  his 
product  "Roman  Cement."  In  1824,  Joseph  Aspdin  of  Leeds, 
England,  patented  a  process  of  manufacture  of  "Portland 
Cement." 

2.  The  cements  in  general  use  in  the  United  States  to-day 
are  of  two  kinds,  Portland  cements  and  natural  cements,  and  in 
what  follows  our  attention  will  be  directed  almost  entirely  to 
1hese  two  products. 

Common  limes  were  formerly  used  largely  in  engineering 
construction,  but  have  of  late  been  almost  entirely  superseded, 


2  CEMENT  AND  CONCRETE 

for  this  purpose,  by  cements.  Since  the  hardening  of  lime 
mortar  depends  on  the  absorption  of  carbonic  acid  from  the 
atmosphere,  these  limes  are  sometimes  called  "air  limes/'  while 
the  hydraulic  products  which  set  under  water  are,  for  a  similar 
reason,  styled  "water  limes."  Hydraulic  limes,  though  playing 
an  important  role  in  foreign  countries,  are  not  manufactured  or 
used  to  any  extent  in  the  United  States.  The  European  prod- 
uct known  as  "Roman"  or  "Vassy"  cement,  somewhat  re- 
sembles our  natural  cement,  but  is  usually  inferior  to  the  Ameri- 
can article.  Our  chief  interest  in  these  products,  which  are  used 
only  abroad,  is  to  know  what  relation  they  bear  to  the  cements 
with  which  we  are  familiar.  The  following  classifications  are 
selected  as  being  authoritative: 

3.  The  conferences  of  Dresden  (1886)  and  Munich  (1884)  on 
Uniform  Methods  of  Testing  for  Materials  of  Construction,  clas- 
sified the  hydraulic  products  as  follows :  - 

(1)  Hydraulic  limes:  made  by  roasting  either  argillaceous  or 
siliceous  limestones.     They  slake  partially  or  wholly  on  the  ad- 
dition of  water. 

(2)  Roman  cements:  made  from  argillaceous  limestones  hav- 
ing a  large  proportion  of  clay.     They  do  not  slake  by  the  addi- 
tion of  water  and  hence  must  be  mechanically  ground  to  powder. 

(3)  Portland  cements:  obtained   by  burning  to  the  point   of 
insipient  vitrification  either  hydraulic  limestones  or  mixtures  of 
argillaceous  materials  and  limestones,   and  afterward  grinding 
the  product  to  fine  powder. 

(4)  Hydraulic  gangues:  natural  or  artificial  materials  which 
do  not  harden  alone,  but  which  furnish  hydraulic  mortars  when 
mixed  with  quicklime. 

(5)  Pozzolana   cements    produced    by    an    intimate    mixture 
of  powdered  hydrate  of  lime  and  finely  pulverized  hydraulic 
gangues. 

(6)  Mixed  cements:    the    products  of   intimate    mixtures    of 
manufactured  cement  with  certain  materials  proper  for  such  a 
purpose.     Mixed  cements  should  always  be  designated  as  such 
and  the  materials  entering  into  the  composition  should  be  stated, 
but   it  may  be   added    parenthetically  that   these    things    are 
seldom  done. 

4.  MM.  Durand-Claye  and  Debray  divide  cements  into  six 
classes,  namely,  (1),  Grappier  cements  —  obtained  by  grinding 


LIME  3 

the  pieces  of  hydraulic  lime  which  do  not  slake;  (2),  quick-set- 
ting (Vassy)  cements  —  formed  by  burning  very  argillaceous 
limestones  at  a  low  temperature;  (3),  natural  Portland  cements, 
or  those  cements  made  from  natural  rock  which  correspond  to 
artificial  Portland  in  character;  (4),  mixed  cements;  (5),  arti- 
ficial Portlands;  and  (6),  slag  cements. 

M.  H.  LeChatelier,  an  eminent  French  authority,  divides 
hydraulic  products  into  four  classes,  namely : l  —  Portland  ce- 
ments, hydraulic  limes,  natural  cements,  and  mixed  cements.  Ho 
subdivides  the  third  class,  natural  cements,  into  quick-setting, 
slow-setting  and  grappier  cements,  and  includes  natural  Port- 
lands among  the  slow-setting  natural  cements.  Slag  cements, 
which  are  put  in  a  separate  class  by  MM.  Durand-Claye  and 
Debray,  are  included  in  "mixed  cements"  by  M.  LeChatelier. 

5.  Prof.  I.  0.  Baker   gives   a  classification    that    is    better 
adapted  for  use  in  this  country  than  any  of  the  above.2     He 
divides  the  products  obtained  by  burning  limestone,  either  pure 
or  impure,  into  lime,  hydraulic  lime  and  hydraulic  cements.     He 
then  sub-divides  cement  into  Portland,   Rosendale  (preferably 

called  natural)  and  Pozzolana. 

0 

ART.  2.    LIME:   COMMON  AND  HYDRAULIC 

6.  Common  lime  is  the  product  obtained  by  burning  a  pure, 
or  nearly  pure,  carbonate  of  lime.     On  being  treated  with  water 
it  slakes  rapidly,  evolving  much  heat  and  increasing  greatly  in 
volume.     It  is  now  seldom  used  in  engineering  construction  and 
will  not  be  considered  further. 

7.  Prof.  M.  Tetmajer  has  thus  denned  hydraulic  limes:  Hy- 
draulic limes  are  the  products  obtained  by  the  burning  of  argil- 
laceous or  siliceous  limestones,  which,  when  showered  with  water, 
slake    completely    or   partially    without   sensibly    increasing   in 
volume.    According  to  local  circumstances,  hydraulic  limes  may 
be  placed  on  the  market  either  in  lumps,  or  hydrated  and  pul- 
verized.    The  following  table  gives  a  classification  of  hydraulic 
limes  according  to  M.   E.  Candlot  f  who  states  that  the  first 


1  "Tests  of  Hydraulic  Materials,"  by  H.  LeChatelier.     Trans.  Am.  Inst. 
Mining  Engrs.,  1893. 

2  •" Masonry  Construction,"  p.  48. 

3  "Ciments  et  Chaux  Hydrauliques,"  par  E.  Candlot. 


CEMENT  AND  CONCRETE 


class  is  seldom  used  for  important  work  and  that  the  fourth 
class  is  quite  rare. 

TABLE  1 
Classification  of  Hydraulic  Limes.     E.  Candlot 


Class. 

Per  Cent, 
of  Clay  in 
Limestone. 

Per  Cent, 
of  Silica 
and  Alumi- 
na in  Fin- 
ished Prod- 
uct. 

Hydraulic 
Index,  or 
Ratio  of 
Silica  and 
Alumina  to 
Lime. 

Approx. 
Time  to 
Set, 
Days. 

Feebly  Hydraulic  Lime 
Ordinary      "             " 
Real              "             " 

5  to     8 
8  to  15 
15  to  19 

9  to  14 
14  to  24 
24  to  30 

.10  to  .16 
.16  to  .31 
.31  to  .42 

16  to  30 
10  to  15 
5  to     9 

Eminently    "             " 

19  to  22 

80  to  33 

.42  to  .50 

2  to     4 

Hydraulic  limes  should  be  burned  slowly,  and  at  such  a  tem- 
perature that  sintering  does  not  take  place.  The  best  hydraulic 
limes  have  a  composition  very  similar  to  that  of  Portland  cement. 
The  comparatively  low  temperature  at  which  they  are  burned 
permits  them  to  slake  on  the  addition  of  water.  They  gain 
strength  much  more  slowly  than  cements. 

Having  considered  the  classification  of  hydraulic  products  as 
a  whole,  we  may  proceed  to  the  discussion  of  Portland  and  nat- 
ural cements,  the  hydraulic  products  which  have  by  far  the 
greatest  importance  here,  and  the  only  varieties  which  will  be 
taken  up  in  detail  in  the  present  work. 

ART.  3.    PORTLAND  CEMENT 

8.  As  the  classification  of  hydraulic  products  varies,  so  do 
opinions  vary  as  to  what  shall  be  included  under  the  name  Port- 
land cement.  There  seems  to  be  agreement  on  at  least  one 
point,  namely,  that  the  burning  shall  be  carried  to  a  point  just 
short  of  vitrification.  Ideas  concerning  other  points  are  crys- 
tallizing rapidly.  The  Association  of  German  Portland  Cement 
Manufacturers  has  given  a  definition  of  Portland  cement  in  a 
practical  manner  by  binding  its  members  "to  produce  under 
the  name  of  Portland  cement  only  such  an  article  as  is  made  by 
calcining  a  thorough  mixture,  consisting  essentially  of  calcare- 
ous and  clayey  substances,  and  then  grinding  the  same  to  the 
fineness  of  flour;"  and  they  further  declare  that  "any  article 
made  in  a  manner  differing  from  the  above  method,  or  to  which 
during  or  after  burning  any  foreign  substances  have  been  added/' 


PORTLAND  CEMENT  5 

is  not  recognized  by  them  as  Portland  cement,  and  the  sale  of 
such  products  under  the  designation  "Portland  Cement"  is  re- 
garded by  them  as  defrauding  the  purchaser.  This  declaration 
does  not  apply  to  such  minor  additions  as  are  made  to  regulate 
the  setting  time  of  Portland  cement,  and  which  are  permitted 
to  an  extent  of  2  per  cent." 

9.  M.  LeChatelier  has  given  the  following  limits  for  the 
amounts  of  the  materials  usually  contained  in  good  commercial 
Portland  cements : l  - 

Silica 21  per  cent,  to   24  per  cent. 


Alumina 6 

Oxide  of  Iron 2 

Lime      60 

Magnesia .5 

Sulphuric  Acid 5 

Water  and  Carbonic  Acid  .        1 


8 
4 

65 
2 

1.5 
3 


The  upper  limit  for  lime  (65  per  cent.)  is  being  exceeded  in  re- 
cent years. 

These  substances  occur  as  "(1)  SiO2,  3CaO,  the  essentially 
cementitious  ingredient;  (2)  A12O3,  3CaO,  the  substance  mainly 
active  during  setting  and  contributing  somewhat  to  the  subse- 
quent hardening;  and  (3)  a  fusible  calcium  silico-aluminate 
whose  chief  function  is  that  of  a  flux  during  burning  to  promote 
the  necessary  chemical  reactions."  2  M.  LeChatelier  further 
holds  that  in  good  Portland  cements  the  following  formulas 

should  be  true: 

CaO,  Mg  O    < 
SiO2  +  A12O3-3' 
and 

CaO,  MgO  > 


SiO2  -  (A12O3,  Fe2O3)  =    ' 

in  each  case  the  quantities  in  the  formulas  being  equivalents  of 
the  substances,  not  weights.  The  ratio  of  the  acid  constitu- 
ents, silica  and  alumina,  and  the  basic  constituents,  lime  and 
magnesia,  is  called  the  hydraulic  index.  Although  these  form- 
ulas have  been  quite  generally  accepted  as  properly  fixing  the 
limit*  of  the  ingredients  it  maybe  noted  that  they  are  based  on 
the  assumption  that  SiO2,  and  A12O3?  are  equally  capable  of  dispos- 


1  "Tests  of  Hydr.  Materials,"  Tr.  Am.  Tnst.  Mining  Engrs.,  1893. 

2  Jour.  Soc.  Ch.  Ind.,  Mar.  31,  1891,  p.  256. 


6 


CEMENT  AND  CONCRETE 


ing  of  a  given  quantity  of  lime  and  magnesia,  and  it  is  thought 
by  some  authorities  that  the  assumption  is  not  warranted. 

In  the  Journal  Society  Chemical  Industry,  1897,  Messrs.  S. 
B.  and  W.  B.  Newberry  give  the  results  of  some  investigations 
in  this  line  from  which  they  concluded  that  the  essential  in- 
gredient of  Portland  cement  is  a  tri-calcium  silicate,  but  that 
the  alumina  occurs  as  a  dicalcic  aluminate.  They  therefore 
considered  that  the  per  cent,  of  lime  should  equal  2.8  times  the 
per  cent,  of  silica  plus  1.1  times  the  per  cent,  of  alumina. 

10.  The  following  analyses  of  brands  in  the  market  are  se- 
lected from  the  various  sources  indicated  in  the  table.  They 
are  given  here  merely  to  illustrate  the  proportions  obtaining  in 

commercial  products. 

TABLE     2 

Analyses    of    Portland   Cements 


BRAND. 

Si02. 

Ai2O3. 

Fe203. 

CaO. 

MgO. 

Nti20 
K2O. 

S03. 

HSO  & 

Loss. 

1.  Alpha 

20.38 

63.30 

2.86 

1.13 

1.75 

2.  Atlas 

21.30 

7.65 

'2.85 

60.95 

2.95 

1.15 

1.81 

1.41 

3.  Bronson 

22.90 

6.80 

3.60 

63.90 

0.70 

1.10 

0.40 

0.60 

4.  Buckeye 

21.30 

6.95 

2.00 

62.30 

1.20 

0.98 

4.62 

5.  Empire 

22.04 

6.45 

3.41 

60.92 

3.53 

2.25 

6.   Wyandotte 

23.20 

8.00 

2.40 

62.10 

2.00 

0.80 

7.  Omega 

22.24 

7.26 

2.54 

64.96 

2.26 

0.41 

0.33 

8.  Yankton 

7.70 

4.80 

60.00 

0.80 

1.20 

9.   Giant 

23.36 

8.07 

4.83 

58.93 

1.00 

0.50 

0.50 

2.46 

10.  Medusa 

23.20 

7.03 

2.41 

64.19 

0.97 

2.20 

11.  Dyckerhoff 

19.35 

7.00 

4.50 

63.75 

5.40 

12.   German  i  a 

21.14 

6.30 

2.50 

66.04 

1.11 

2.91 

13.  Alsen's 

24.90 

8.00 

3.22 

59.38 

0.38 

0.75 

0.98 

2.16 

14.  Alsen's 

23.30 

5.85 

4.65 

60.90 

0.90 

0.30 

2.43 

1.40 

3RAND. 

AUTHORITY. 

RAW  MATERIALS. 

LOCATION.    - 

1 

"  Directory  Amer'n 

Cement  Rock  and  Limestone 

Alpha,  N.J. 

Cement  Industries" 

2 

u 

11                 11           H                  tt 

Northampton,  Pa. 

3 

II 

Marl  and  Clay 

Bronson,  Mich. 

4 

It 

U              it         tt 

Bellefontaiue,  Ohio. 

5 

tt 

It          tt       It 

Warners,  N.Y. 

6 

1C 

Soda  Ash  Waste  and  Clay 

Wyandotte,  Mich. 

7 

u 

Marl  and  Clay 

Jonesville,  Mich. 

8 

ti 

Chalk  and  Clay 

Yankton,  S.  Dakota. 

9 

U.  Cummings 

Cement  Rock  and  Limestone 

Egypt,  Pa. 

"  Amer'n  Cements" 

10 

U                            It 

Marl  and  Clay 

Sandusky,  Ohio. 

11 

U                           U 

Limestone,  Marl  and  Clay 

Ainoeneburg,  Ger. 

12 

41                            (( 

Marl  and  Clay 

Lehrte,  Germany. 

13 

U                            U 

Chalk  and  Clay 

Itzehoe,  Germany. 

14 

"Richard  K.  Meade, 

Chalk  and  Thames  Mud 

England. 

"Exam,  of  P.  Cem." 

SLAG  CEMENT  7 

ART.  4.     SLAG  CEMENT 

11.  Slag   cement    is  manufactured  to  a  considerable  extent 
in  Europe  and  is  beginning  to  assume  some  importance  in  the 
United  States.     It  is  a  pozzolana  cement  in  which  the  silica 
ingredient   is   supplied   by   blast    furnace   slag.     Pozzolana   ce- 
ments have  been  defined  as  "  products  obtained  by  intimately 
and  mechanically  mixing,  without  subsequent  calcination,  pow- 
dered hydrates  of  lime  with  natural  or  artificial  materials  which 
generally  do  not  harden  under  water  when  alone,   but  do  so 
when  mixed  with  hydrates  of  lime  (such  materials  being  pozzo- 
lana, Santorin  earth,  trass  obtained  from  volcanic  tufa,  furnace 
slag,  burnt  clay,  etc.),  the  mixed  product  being  ground  to  ex- 
treme fineness."1 

Slag  cement  somewhat  resembles  Portland  in  its  properties,  but 
is  more  like  some  of  the  natural  cements  in  its  constituents,  while 
the  manner  of  occurrence  of  these  constituents  and  the  method 
of  manufacture  are  quite  different  than  in  either  of  these 
classes. 

12.  As  this  cement  is  a  mixture  of  lime  and  pozzolanic  ma- 
terials, its  value  depends  largely  upon  its  extreme  fineness  and 
the  intimate  mixture  of  the  ingredients.     Its  specific  gravity  is 
low,  about  2.7  to  2.8,  and  it  sets  very  slowly,  although  the 
setting  may  be  hastened  by  the  addition  of  certain  substances 
such  as  caustic    soda.     On  account  of    the  sulphide  present, 
most  slag  cements  are  not  suited  to  use  in  air,  as  they  crack 
and  soften  in  this  medium;  neither  are  they  suitable  for  use  in 
sea  water,  nor  in  freezing  weather,  but  when  mixed  with  two 
or  three  parts  sand  and  kept  constantly  wet  with  fresh  water, 
they  give  quite  satisfactory  results. 

Slag  cement  has  an  approximate  composition  of  silica,  20  to 
30  per  cent.,  alumina,  10  to  20  per  cent.,  and  lime,  40  to  50  per 
cent.  It  usually  contains  calcium  sulphide,  the  amount  some- 
times reaching  three  or  four  per  cent.  The  characteristic  green- 
ish tint  which  slag  cements  exhibit  when  they  harden  in  water 
is  due  to  this  ingredient,  as  is  the  odor  of  hydrogen  sulphide 
sometimes  given  off  by  a  briquet  when  broken,  especially  if  it 


1  "  Report  of  Board  of  Engineers  on  Steel  Portland  Cement,"  Washing- 
ton, 1900. 


8 


CEMENT  AND  CONCRETE 


has  hardened  in  sea  water, 
a  percentage  of  magnesia.1 


Some  slag  cements  have  also  quite 


ART.  5.     NATURAL  CEMENT 

13.  Natural  cement,  as  its  name  implies,  is  made  from  rock 
as  it  occurs  in  nature.  Argillaceous  limestones,  magnesian  lime- 
stones, or  argillo-magnesian  limestones,  having  the  proper  pro- 
portion of  clay,  magnesia  and  lime,  may  be  used  for  the 
production  of  natural  cement.  The  burning  is  not  carried  so 
far  as  in  the  manufacture  of  Portland  cement,  and  the  resulting 

TABLE    3 
Analyses  of  Natural  Cements 


j 

<j       K 

jjj 

IB 

POTASH 

*     0     *     T 

REFER- 

SILICA. 

3 

IRON 
OXIDE. 

LIME. 

fe 

o 

AND 

|     §     g     1 

ENCE. 

1 

SODA. 

£*•** 

c 

d 

e 

/ 

9 

h 

i 

1 

24.30 

2.61 

6.20 

39.45 

6.16 

5.30 

15.23 

2 

34.66 

5.10 

1.00 

30.24 

18.00 

6.16 

4.84 

3 

23.16 

6.33 

1.71 

36.08 

20.38 

5.27 

7.07 

4 

26.40 

6.28 

LOO 

45.22 

9.00 

4.24 

7.86 

5 

27.30 

7.14 

1.80 

35.98 

18.00 

6.80 

2.98 

6 

27.98 

7.28 

1.70 

37.59 

15.00 

7.96 

2.49 

7 

27.69 

8.64 

2.00 

42.12 

14.55 

2.00 

3.00 

8 

27.60 

10.60 

0.80 

33.04 

7.26 

7.42 

2.00 

9 

28.02 

10.20 

8.80 

44.48 

1.00 

0.50 

7.00 

PLACE  OF 

REFER- 

BRAND. 

MANUFACTURE. 

ENCE. 

a 

b 

1 

Buffalo 

Buffalo,  N.  Y. 

2 

Utica 

Utica,  111. 

3 

Milwaukee 

Milwaukee,  Wis. 

4 

Louisville 

Louisville,  Ky. 

5 

Hoffman 

Rosendale,  N.  Y. 

6 

Norton  High  Falls 

Rosendale,  N.  Y. 

7 

Akron 

Akron,  N.  Y. 

8 

Utica 

LaSalle,  111. 

9 

Round  Top 

Hancock,  Md. 

Selected  from  table  compiled  by  Mr.  U.  Cuinmings,  "  Brickbuilder, "  May,  1895. 


1  For  an  excellent  resume  of  the  qualities  and  distinguishing  character- 
istics of  slag  cements,  the  reader  is  referred  to  "  Report  of  Board  of  Engi- 
neers on  Steel  Portland  Cement  as  used  in  United  States  Lock  at  Plaque- 
mine,  La."  Washington,  1900. 


NATURAL  CEMENT  9 

product  is  of  lighter  weight  and  usually  quicker  setting,  though 
some  natural  cements  are  quite  slow  setting.  The  properties  of 
these  cements,  coming  from  different  localities,  vary  greatly. 
In  fact,  it  is  difficult  to  distinguish  some  natural  cements  from 
Portland,  and  they  may  be  considered  to  grade  into  the  natural 
Portlands.  Light  burning  in  manufacture,  light  weight  per  cubic 
foot,  and  slower  rate  of  acquiring  strength,  may  be  considered 
the  distinguishing  characteristics  from  a  physical  point  of  view. 

14.  Analyses.  —  Table  3  gives  the  results  of  a  number  of 
analyses  of  natural  cement,  selected  from  a  table  compiled  by 
Mr.  U.  Cummings. 

Comparing  these  analyses  with  those  given  for  Portland  ce- 
ment in  Table  2,  it  is  seen  that  natural  cements  have  a  higher 
percentage  of  silica,  about  the  same  amount  of  alumina,  and  a 
much  smaller  content  of  lime,  than  have  Portlands.  Many  natu- 
ral cements  have  a  large  percentage  of  magnesia,  but  the  mag- 
nesia and  lime  together  of  natural  cements  usually  do  not  equal 
the  percentage  of  lime  in  Portlands.  In  other  words  the  hy- 
draulic index  is  usually  higher  than  in  Portland  cements. 


CHAPTER  II 

MANUFACTURE 

ART.  6.   THE  MANUFACTURE  OF  PORTLAND  CEMENT 

15.  Historical.  —  It  is  said  that  as  early  as  1810  a  patent 
was  obtained  in  England  for  the  manufacture  of  an  artificial 
product  by  calcining  a  mixture  of  carbonate  of  lime  and  clay. 
This,  however,  was  not  called  cement,  and  it  was  not  until  1824 
that  Joseph  Aspdin,  of  Leeds,  England,  in  obtaining  a  patent 
for  the  manufacture  of  a  similar  material,  called  his  product 
"  Portland  Cement."     This  name  was  probably   suggested  by 
the  fact  that  the  color  of  the  hardened  product  resembled  that 
of  a  limestone  quarried  on  the  Island  of  Portland.     The  industry 
was  introduced  into  Germany  about  thirty  years  later,  and  has 
since  grown  to  very  substantial  proportions  in  both  of  these 
countries,  as  well  as  in  France,  Austria  and  Russia. 

David  O.  Saylor  was  the  first  to  manufacture  Portland  ce- 
ment in  the  United  States,  at  Coplay,  Pa.,  about  1872,  and 
works  were  established  at  that  point  in  1875.  These  were 
soon  followed  by  other  factories  in  Pennsylvania  and  Indiana, 
and  at  present  cement  is  successfully  manufactured  in  nearly 
half  of  the  states  of  the  Union,  the  production  having  steadily 
increased. 

16.  MATERIALS  REQUIRED. —The  materials  requisite  for  the 
manufacture    of   Portland   cement   are   carbonate   of  lime   and 
silica.      The  former  may  be  in  the  form  of  limestone,   chalk, 
or  calcareous  marl,  the  last  two  being  preferable  on  account  of 
greater  ease  of  working.      The  silica   may  be  in  the  form  of 
shale  or  clay,  the  latter  to  be  preferred.     The  clay  need  not  be 
entirely  free  from  impurities,  but  it  should  not  contain  any  con- 
siderable amount  of  sand,  for  although  silica  is  the  most  useful 
constituent  of  the  clay,  it  must  not  be  in  this  insoluble  form. 
Although  formerly  authorities  did  not  agree  as  to  whether  the 
alum'na  in  the  clay  was  an  unwelcome  constituent  for  Portland 
cement  manufacture,  it  is  now  considered  that  the  dicalcic  or 

10 


PORTLAND  CEMENT 


11 


tricalcic  aluminate  formed  plays  a  role  in  the  setting  of  the 
cement,  and  possibly  also  in  the  subsequent  hardening. 

A   few  analyses  of  materials  suitable  for  Portland  cement 
manufacture  are  given  in  Table  4. 

TABLE   4 

Analyses  of  Cement  Materials 


MATERIALS. 

SiO,. 

A1203 
and 
Fe203. 

CaC03. 

MgC03. 

S03. 

Water 
and 
Loss. 

White  Marl,  Empire  l  .  .  . 
Clay,  Empire  l  
Gray  Marl  .  

.26 

40.48 
7.26 

.10 
20.95 
1  49 

94.39 
25.80 
84  10 

.38 
.99 
.91 

.  .  . 

3.10 
8.50 
3  98 

Clay  

53  5 

24.20 

5.15 

2.1') 

14.10 

Limestone,  Glens  Falls1  .  . 
Clay,  Glens  Falls1  .... 
Gray  Chalk  Medway  Eng  2 

3.30 
56.27 
5  45 

1.30 
28.15 
3  87 

93.13 
10.43 
88  72 

1.58 
2.25 

0.30 
0.12 

liiver  Mud  Medway  Enfr.* 

71  71 

16  70 

4  0") 

1 "  Manufacture  Portland  Cement  in  New  York  State/'  by  Mr.  Edwin  C. 
Eckel,  C.  E. 

2  "  Cement  for  Users,"  Mr.  Henry  Faija. 

17.  The  materials  for  Portland  cement  manufacture,  lime- 
stone, marl,  clay,  shale,  etc.,  are  widely  disseminated,  but  the 
suitability  of  a  certain  locality  for  successful  commercial  manu- 
facture depends  upon  the  manner  of  occurrence  of  these  requi- 
sites. In  England  the  clay  is  dug  from  the  old  beds  of  the 
Thames  and  Medway  Rivers,  and  chalk,  which  occurs  in  abun- 
dance, furnishes  the  carbonate  of  lime  in  most  cases,  though 
limestone  is  sometimes  used.  In  Germany  both  chalk  and 
marl  are  used;  the  chalk  being  a  soft  white  marl  similar  to  the 
deposits  in  this  country,  and  the  marl  a  "more  or  less  hard 
limestone  rock  containing  clay."  In  the  United  States  both 
limestones  and  marls  are  used.  The  most  important  cement 
producing  egion  in  the  United  States  is  in  the  Lehigh  Valley, 
where  an  argillaceous  limestone  is  employed.  The  factories 
using  marl  are  situated  in  New  York,  Ohio,  Indiana,  Michigan, 
etc.,  where  the  marl  is  found  overlying  beds  of  clay  suitable  for 
cement  making.  In  the  Lehigh  Valley  region  many  advan- 
tages are  combined.  The  cement  rock  of  that  locality  has 
nearly  the  correct  composition  for  Portland  cement  manufac- 


12  CEMENT  AND  CONCRETE 

ture.  The  supply  of  this  rock  is  almost  inexhaustible,  the  man- 
agers of  the  works  have  had  long  experience  in  the  production 
of  cement  from  these  materials,  and  a  market  for  the  product  is 
near  at  hand. 

Deposits  of  cement  materials  are  of  value  only  when  the 
limestone  or  marl,  and  clay  or  shale,  are  found  in  large  quanti- 
ties and  near  together,  when  the  physical  character  of  the  ma- 
terials is  such  as  to  render  them  easy  of  comminution  and  mix- 
ture, when  coal  or  other  suitable  fuel  may  be  had  at  low  prices, 
and  when  the  market  is  not  too  far  removed. 

The  following  estimate  of  the  relative  quantities  of  cement 
made  in  the  United  States  in  1902  from  the  several  classes  of 
materials  has  been  made  by  Mr.  E.  C.  Eckel : * 

Argillaceous  limestone  and  pure  limestone      ....  68  Per  cent. 

Marl  and  clay 14       " 

Soft  limestone  and  clay 4^     " 

Hard  limestone  and  clay  .  .          13£     " 

18.  GENERAL  DESCRIPTION  OF  PROCESSES.  The  essentials 
of  any  method  of  Portland  cement  manufacture  are  that  the 
materials  shall  be  correctly  proportioned,  very  finely  comminuted 
and  thoroughly  mixed,  that  the  mixture  shall  be  carefully 
burned  to  just  the  proper  degree  of  calcination  and  the  result- 
ing clinker  ground  to  extreme  fineness.  How  these  essentials 
can  be  best  accomplished  depends  upon  the  character  of  the 
raw  materials  and  the  cost  of  fuel  and  labor,  so  that  the  de- 
tails of  the  method  vary  with  the  materials  used  and  with  the 
local  conditions. 

In  order  that  the  proportions  may  be  accurately  determined, 
it  is  usually  necessary  to  dry  one  or  both  of  the  raw  materials. 
The  ingredients  may  be  ground  separately  and  afterward  mixed, 
though  with  certain  materials  the  grinding  and  mixing  may  be 
done  at  the  same  time.  In  this  mixing,  a  large  amount  of  water 
may  be  used,  as  in  the  "wet  process,"  giving  a  very  thin  slurry; 
a  moderate  amount  may  be  used,  as  in  the  semi-wet  process,  giv- 
ing a  slurry  of  creamy  consistency;  or  the  dry  process  may  be 
employed,  where  the  amount  of  water  used  is  no  more  than 
sufficient  to  dampen  the  materials.  The  burning  may  be  ac- 


Engineering  News,  April  16,  1903. 


PORTLAND   CEMENT  13 

complished  in  any  one  of  several  styles  of  kiln,  the  selection 
depending  upon  the  relative  cost  of  labor  and  fuel,  the  relative 
necessity  of  economy  and  rapid  production,  and,  perhaps  we 
should  add,  the  rigidity  of  the  specifications  which  the  finished 
product  must  fulfill.  The  grinding  is  a  simple  mechanical  prob- 
lem, to  secure  the  required  degree  of  fineness  with  least  cost. 

19.  THE  WET  PROCESS.     Although  an  excess  of  water  may 
be  used  to  mix  materials  that  require  previous  grinding,  the  wet 
process  is  particularly  adapted  to  such  raw  materials  as  are  easily 
acted  upon  by  water.     This  method  was  developed  in  England, 
where  it  is  still  employed  to  some-  extent  and  it  has 'been  used 
in  this  country  as  well. 

Proper  amounts  of  the  raw  materials,  previously  ground  if 
necessary,  are  placed  in  a  wash  mill  with  a  large  amount  of 
water.  The  wash  mill  is  a  circular  trough  in  which  teeth  or 
arms  are  made  to  revolve,  agitating  the  mass.  When  the  mate- 
rials are  so  finely  divided  as  to  be  held  in  suspension,  the  thin 
slurry  is  run  off  into  "  backs, "  or  shallow  settling  reservoirs, 
where  the  solid  matter  settles;  the  clear  liquid  is  then  run  off, 
the  slurry  being  allowed  to  dry  further  until  it  can  be  cut  into 
bricks  and  placed  on  drying  floors  artificially  heated.  The 
bricks  are  then  taken  to  the  burning  kilns  and  finally  ground  to 
form  the  finished  product. 

The  disadvantages  of  this  method  are  that  much  space  is 
required  for  the  settling  floors,  the  amount  of  heat  required  to 
dry  the  brick  is  excessive,  and  the  process  is  necessarily  slow. 
These  disadvantages  are  so  great  that  the  method  above  outlined 
is  rapidly  falling  into  disuse.  Materials  particularly  adapted  to 
wet  mixing  are  still  treated  by  this  process,  but  the  wet  mixture 
is  run  directly  into  very  long  rotary  kilns  and  is  dried  in  passing 
through  the  first  half  of  the  length,  which  is  heated  by  the  gases 
from  the  lower  portion  where  the  burning  is  completed. 

20.  THE  DRY  PROCESS.     This    method    of    manufacture    is 
best  adapted  to  materials,  such  as   limestone  and  shale,  that 
must  be  dried  and  ground  before  they  can  be  mixed.     The  rock 
as  it  comes   from   the   quarry  is   first  passed   through  a  rock 
crusher,  reducing  it  to  the  size  of  broken  stone  used  for  con- 
crete; then  to  some  other  form  of  crusher,  such  as  heavy  rolls, 
until  it  is  reduced  to  pieces  about  one-half  inch  or  less  in  size. 
It  is  then  dried  by  artificial  heat. 


14  CEMENT  AND  CONCRETE 

The  materials  may  now  be  combined  in  proper  proportions 
and  ground  together  to  extreme  fineness,  thereby  becoming 
thoroughly  mixed.  If  the  mixture  is  to  be  burned  in  the  old 
style  kiln,  it  must  now  be  dampened  so  that  it  may  be  pressed 
into  bricks  to  be  charged  in  the  kiln.  If  a  rotary  kiln  is  used, 
however,  the  dry  mixture  may  be  fed  directly  into  it,  or  it  may 
be  moistened  enough  so  that  it  will  form  into  little  lumps  the 
size  of  wheat  grains,  and  these  fed  to  the  rotary. 

21.  THE  SEMI-DRY  PROCESS.  The  two  processes  briefly  de- 
scribed above  are  extremes  admitting  many  modifications  which 
will  not  be  entered  into  in  detail.  What  may  be  called  the 
semi-dry  process,  however,  has  been  so  widely  used  in  the 
United  States  that  it  deserves  some  special  mention,  and  it  may 
perhaps  be  best  explained  by  giving  the  method  formerly  em- 
ployed in  a  well-known  American  factory  which,  until  a  few 
years  ago,  was  using  the  vertical  kiln. 

The  carbonate  of  lime  in  the  form  of  marl  was  found  above 
the  clay  in  beds  varying  in  thickness  up  to  20  feet.  The  clay 
in  general  contained  little  sand,  and  the  beds  were  of  such 
thickness  that  whenever  too  much  sand  was  present,  the  clay 
might  be  wasted.  The  materials  were  delivered  to  the  factory, 
about  three-quarters  of  a  mile  from  the  deposit,  by  small  cars 
running  on  a  narrow  gage  railroad. 

When  the  clay  reached  the  factory  it  was  put  in  shallow 
wooden  pans  and  run  into  dry  kilns  on  light  cars.  After  dry- 
ing, which  required  36  to  48  hours,  the  clay  was  ground  and  de- 
livered in  weighed  quantities  to  the  mixer.  The  main  object 
of  drying  the  clay  was  to  be  able  to  control  the  amount  added 
to  a  given  quantity  of  marl,  and  the  grinding  was  to  facilitate 
the  mixing  of  the  two  ingredients.  As  the  cars  of  marl  entered 
the  building,  they  were  brought  to  a  given  weight  by  means 
of  a  scale,  which  was  set  and  locked  by  the  manager.  The 
marl  was  then  dumped  directly  into  the  wei  pan  or  mixer. 

The  latter  consisted  of  an  iron  pan,  about  12  feet  in  diameter, 
in  which  revolved  two  cast  iron  rollers  weighing  three  tons 
each.  These  rollers  were  on  opposite  ends  of  a  horizontal  axis 
which  was  attached  to  a  vertical  shaft  in  the  center  of  the  pan. 
This  shaft  being  driven  from  below,  the  rollers  traveled  in  a 
circular  path;  as  the  rollers  were  hung  loose  on  the  horizontal 
axis,  they  revolved  about  the  latter  only  when  sufficient  fric- 


PORTLAND  CEMENT  15 

tion  was  developed  between  their  peripheries  and  the  floor  of 
the  pan.  In  front  of  each  roller  traveled  two  blades,  one  of 
which  pushed  the  material  under  the  roller  from  the  center, 
while  the  other  did  the  same  from  the  circumference. 

A  weighed  amount  of  dry,  powdered  clay  was  admitted  at 
the  side  of  the  mixer,  from  a  hopper  scale,  at  the  same  time  as 
the  marl  was  dumping  into  it,  and  sufficient  water  was  added 
through  a  hose  to  bring  the  contents  of  the  pan  to  a  pasty 
mass.  Five  minutes  were  allowed  for  mixing  each  charge,  when 
a  slide  was  drawn,  leaving  two  holes  in  the  path  of  the  wheels 
and  on  opposite  sides  of  the  pan.  The  material,  or  "mix," 
was  delivered  on  a  belt  conveyor  and  carried  to  a  pug  mill, 
whence  it  issued  in  the  form  of  rough  bricks,  partially  cut  by 
wires  into  six-inch  cubes.  These  cubes,  being  loaded  on  cars, 
were  run  into  the  dry  kiln,  where  they  remained  from  two  to 
four  days,  and  were  then  taken  to  the  kiln  room  to  be  filled,  by 
hand,  into  the  burning  kilns,  which  were  of  the  dome  type. 

In  charging,  layers  of  cement-brick  and  coke  were  alter- 
nated. For  convenience,  as  well  as  to  prevent  the  bricks  being 
crumbled  by  a  fall,  the  charging  was  done  from  three  levels. 
From  36  to  72  hours  were  required  for  burning,  a  charge.  The 
kiln  was  then  opened  at  the  mouth,  and  the  clinker,  which  had 
shrunk  in  volume  about  three-quarters,  and  in  weight  about 
one-half,  was  drawn  off  as  fast  as  it  cooled.  The  clinker  was 
shoveled  from  the  kilns  to  a  pan  conveyor  and  sorted  as  shov- 
eled, only  that  which  appeared  properly  burned  being  allowed 
to  pass;  the  underburned  portion  was  stored  for  further  burn- 
ing, and  the  overburned,  wasted.  Further  sorting  was  done 
by  two  men  stationed  in  the  kiln  room,  who  watched  the 
clinker  as  it  passed  on  the  conveyor  and  picked  out  any  pieces 
defective  in  burn  that  might  have  passed  the  hands  of  the 
shovelers. 

The  conveyor  delivered  the  clinker  to  a  Blake  crusher,  which 
broke  it  into  pieces  the  size  of  pebbles;  thence  it  passed  to 
horizontal  millstones,  or,  to  what  replaced  these,  ball  and 
tube  mills,  for  final  reduction.  The  material  was  then  deliv- 
ered into  cylindrical  screens  having  about  2,500  meshes  per 
square  inch,  that  portion  retained  in  the  screen  being  returned 
to  a  stone  supplied  almost  entirely  with  these  screenings.  The 
cement  was  then  conveyed  to  the  stock  house,  which  was  divided 


16  CEMENT  AND   CONCRETE 

into  bins  of  1,500  barrels  capacity,  and  finally  packed  in  barrels 
by  means  of  a  screw  blade  fitting  the  interior  of  the  barrel. 

22.  DETAILS  OF  THE  MANUFACTURE:  Preparation  and  Mix- 
ing of  the  Raw  Materials.     The  main  points  in  the  preparation 
of  the  raw  materials  for  burning  are :  first,  the  proper  amount  of 
each  ingredient  must  enter  the  mixture;  second,  the  materials 
must  be  reduced  to  an  extremely  fine  state  of  division,  with  no 
lumps;  and  third,  the  mechanical  mixing  must  be  as  perfect  as 
possible.     Unless  the  ingredients   are   dried,   the  first  require- 
ment is  difficult  to  accomplish,  especially  with  marl  and  clay, 
as  the  absorptive  power  of  the  materials  renders  it  difficult  to 
properly    apportion    them.     More    than    three-fourths    of    the 
Portland  cement  manufactured  in  the  United  States  is  made 
from  limestones.     These  must  be  ground  before  they  can  re- 
ceive the  required  addition  of  clay  or  of  purer  limestone,  as  the 
case  may  be,  and  they  are  usually  dried  to  facilitate  the  grind- 
ing as  well  as  to  permit  of  determining  the  correct  proportions 
of  the  ingredients.     These  hard  materials  are  first  crushed  in 
an  ordinary  stone  crusher  or  between  heavy  rolls,  then  dried 
in  rotary  driers,  or  otherwise;  next,  mixed  and  ground  together 
to   an   extreme  .fineness   in  ball   or  tube   mills.     When   rotary 
kilns   are   employed,   the   mix   may   be  burned   dry,   but   with 
fixed  kilns,  it  is  moistened  to  form  bricks  which  are  charged  in 
the  kilns  with  alternate  layers  of  coke. 

Soft  materials,  such  as  marl  and  clay,  are  easy  of  reduc- 
tion in  water,  and  are  naturally  treated  by  the  wet  or  semi- 
dry  process,  although  they  may  be  prepared  by  the  dry  process. 
In  the  former  method  the  grinding  and  mixing  are  accom- 
plished by  edge  runners,  pug  mills  or  wash  mills.  If  the  ma- 
terials have  not  been  dried  before  mixing,  the  mix  or  slurry 
should  be  sampled  and  analyzed  before  it  is  passed  to  the  kilns. 
When  fixed  kilns  are  employed,  it  is  desirable  that  the  bricks 
should  be  as  porous  as  possible,  that  the  fire  may  more  readily 
reach  the  interior  of  the  brick.  It  is  claimed  by  some  manu- 
facturers that  by  spreading  the  slurry  on  a  floor  to  dry,  and 
then  cutting  into  rough  cubes  when  dry  enough  to  be  taken  to 
the  dry  kiln,  more  porous  bricks  are  obtained. 

23.  BURNING:    STYLES  OF  KILNS.      The  various   styles    of 
kilns  in    use    may   be    divided  into   four   classes,  namely:    (1) 
Common  dome  kilns,  (2)  Continuous  kilns,    (3)    Chamber    and 


PORTLAND  CEMENT  17 

ring  kilns,  and  (4)  Rotary  kilns.  The  dome  kiln  is  the 
simplest  type.  The  chamber  is  usually  egg  shaped.  Cement- 
brick  and  coke  are  piled  in  alternate  layers,  the  use  of 
the  proper  amount  of  the  latter  requiring  much  skill,  as  it  is 
a  matter  of  experience.  As  the  draft  in  the  kiln  varies  with 
the  weather,  this  method  of  burning  is  more  or  less  at  the  mercy 
of  the  winds.  When  the  burning  is  complete,  the  kiln  is  al- 
lowed to  cool  before  removing  the  clinker,  and  thus  much  heat 
is  lost,  and  the  lining  of  the  kiln  is  destroyed  by  alternate  heat- 
ing and  cooling.  The  amount  of  underburned  and  over- 
burned  clinker  is  likely  to  be  large.  The  output  is  small,  and 
fuel  expense  high. 

The  Dietsch  kiln  is  one  of  the  best  examples  of  the  second 
type,  or  continuous  kiln.  The  slurry,  in  the  form  of  bricks,  is 
introduced  at  the  base  of  the  stack,  into  what  may  be  called 
the  heating  chamber.  Below  this  there  is  a  right  angle  with  a 
short  horizontal  section,  over  which  the  hot  slurry  is  raked, 
to  fall  into  the  burning  chamber.  The  clinker  in  the  lower 
part  of  the  latter  is  cooled  by  the  air  entering  through  the  grates, 
while  the  slurry  in  the  upper  chamber  is  heated  by  the  gases 
from  the  burning  zone.  At  intervals  a  portion  of  the  clinker, 
partially  cooled,  is  removed  at  the  bottom;  this  causes  a  general 
settlement  in  the  kiln  and  leaves  a  space  at  the  top  of  the  burn- 
ing chamber,  into  which  the  dried  clinker  from  above  is  raked, 
and  more  fuel  added.  This  kiln  uses  small  coal  for  fuel  and  is 
more  economical  than  the  dome  type. 

The  distinguishing  feature  of  the  Schofsr  kiln  is  the  con- 
traction of  the  dome  at  the  point  where  combustion  takes 
place,  concentrating  the  draft  at  this  point.  The  air  entering 
the  shaft  at  the  bottom  cools  the  clinker  already  burned,  while 
the  gases  from  the  clinker  burning  in  the  central  section  serve 
to  dry  the  raw  bricks  above.  Several  kilns  of  this  type  are  in 
successful  operation  in  this  country. 

24.  Chamber  kilns  are  used  largely  in  England  with  coke  as 
fuel.  The  gases  from  the  kiln  are  made  to  pass  over  the  slurry 
spread  on  brick  floors,  the  kiln  proper  being  at  one  end  of  this 
chamber  and  the  stack  at  the  other.  These  kilns  are  inter- 
mittent, have  a  comparatively  small  output,  and  require  con- 
siderable labor. 

The  Hoffman  ring  kiln  consists  of  a  series  of  compartments 


18  CEMENT  AND  CONCRETE 

built  around  a  large  central  stack.  The  chambers  communicate 
by  means  of  flues  in  such  a  way  that  the  smoke  and  hot  gases 
from  one  may  be  passed  through  other  chambers  before  reach- 
ing the  chimney.  The  kiln  may  be  either  "up  draft"  or  "down 
draft/7  according  to  the  direction  in  which  the  heat  is  drawn 
through  the  chamber.  The  compartments*  are  charged  from 
the  sides,  and  when  the  moisture  has  been  driven  off  from  the 
material  in  the  chamber  first  fired,  the  gases  from  this  chamber 
are  passed  through  the  adjacent  chambers,  which  have  in  the 
meantime  been  filled  with  raw  materials.  Although  this  kiln 
is  economical  of  fuel  if  run  continuously,  much  labor  is  re- 
quired to  charge  and  empty  it.  This  type  is  not  used  in  the 
United  States,  though  it  has  been  employed  to  some  extent 
in  Germany. 

25.  Rotary  Kilns.  —  Although  rotary  kilns  for  other  purposes 
had  been  in  use  for  some  time,  the  first  patent  for  a  process  of 
manufacture  of  cement  by  their  use  was  issued  in  1877  to  Mr. 
T.  R.  Crampton.  The  method,  apparently,  did  not  pass  beyond 
the  stage  of  laboratory  experiment  until  1885,  when  Frederick 
Ransome  of  England  patented  a  rotary  kiln,  which,  however, 
required  many  important  modifications  to  make  it  a  success. 

About  1888  Mr.  J.  G.  Sanderson  and  Dr.  Geo.  Duryee  made 
some  successful  experiments  with  the  rotary  kiln  for  wet  mix- 
tures, and  in  the  following  year  experiments  were  begun  at  the 
works  of  the  Atlas  Portland  Cement  Co.  under  Mr.  P.  Giron, 
which  resulted  in  the  construction  of  a  practical  kiln  for  burning 
dry  mixtures.  Prof.  Spencer  B.  Newberry,  at  about  the  same 
time,  perfected  the  rotary  process  for  wet  materials  at  Warners, 
N.  Y.,  and  Sandusky,  Ohio. 

A  rotary  kiln  as  used  for  the  burning  of  cement  consists  of  a 
steel  cylinder  five  feet  to  six  and  a  half  feet  in  diameter  and 
about  sixty  feet  in  length.  This  cylinder  is  lined  with  fire- 
brick, rests  on  rollers  with  its  axis  slightly  inclined  to  the  horir 
zontal,  and  is  revolved  slowly  by  means  of  gearing.  The  mix- 
ture to  be  burned  is  introduced  at  the  upper  end  of  the  cylinder, 
while  a  jet  of  gas,  crude  oil,  or  more  frequently,  powdered  coal, 
is  injected  through  a  special  burner  at  the  lower  end.  As  the 
cylinder  revolves,  the  material  works  slowly  toward  the  lower 
end,  the  clinkering  temperature  being  maintained  throughout 
about  the  lower  third  of  the  length.  In  some  of  the  more  elab- 


PORTLAND  CEMENT 


19 


orate  styles,  the  clinker  is  passed  through  one  or  more  cooling 
cylinders  before  it  is  conveyed  to  the  grinding  machinery.  In 
the  Hurry  and  Seaman  rotary,  the  clinker,  after  it  leaves  the 
first  cooling  cylinder,  is  passed  between  rolls  that  serve  to  break 
any  large  lumps,  and  is  moistened  with  water  before  its  passage 
through  the  second  cooling  cylinder,  which  delivers  the  clinker 
warm,  moist,  and  in  small  pieces. 

The  lining  of  rotary  kilns  has  given  much  trouble,  as  the 
clinker  acts  upon  fire  brick  lining  to  form  a  fusible  compound 
at  the  high  temperatures  required  in  the  burning.  One  method 
of  overcoming  this  difficulty  is  to  fuse  upon  the  fire  brick  a  coat- 
ing of  clinker  which  is  beaten  down  while  still  plastic,  so  that  it 
adheres  to  the  brick  and  protects  them  more  or  less  successfully 
from  further  injury.  The  kind  of  fuel  and  the  burner  giving 
the  best  result  have  also  received  much  attention;  while  petro- 
leum was  first  tried  and  is  still  used  to  some  extent,  powdered 
coal  is  now  more  commonly  employed,  and  one  of  the  most  suc- 
cessful forms  of  burner  is  constructed  like  an  injector,  the  pul- 
verized coal  being  drawn  in  with  the  blast  of  air. 

26.  Output  and  Fuel  Consumption  of  Different  Kilns.  —  A 
comparison  of  the  average  output  of  the  several  styles  of  kilns 
described  above,  and  the  approximate  fuel  consumption,  are 
given  in  the  following  table.  Where  it  is  necessary  to  dry  the 
materials  before  introducing  them  into  the  burning  kiln,  the 
fuel  required  in  drying  is  not  included. 


STYLE. 

Barrels  per  Day. 

Fuel  as  Per  Cent, 
of 
Weight  of  Clinker. 

Intermittent  dome 

30 

20  to  30 

Hoffman  (per  chamber)  
Dietsch  and  Schofer 

25 

50  to  75 

15  to  20 
15  to  20 

Chamber  .... 

30 

40  to  50 

Rotary      .... 

120  to  150 

30  to  40 

27.  Advantages  of  the  Rotary  Kiln.  —  Although  the  burning 
of  cement  in  a  rotary  kiln  requires  a  somewhat  larger  fuel  con- 
sumption than  with  some  other  types,  the  ability  to  use  a  cheaper 
form  of  fuel,  and  the  saving  in  the  amount  of  labor  required, 
much  more  than  offset  this  disadvantage.  Either  wet  or  dry 
materials  may  be  fed  to  the  kiln,  thereby  eliminating  the  neces- 
sity of  forming  the  slurry  into  bricks,  drying  and  stacking 


20  CEMENT  AND  CONCRETE 

them  in  the  kilns.  By  the  rotary  process  it  is  possible  to  so 
arrange  a  plant  that  the  material  is  handled  entirely  by  ma- 
chinery from  raw  material  to  finished  product.  The  control 
possible  in  burning  with  the  rotary  is  much  better  than  with 
any  other  style  of  kiln,  as  the  intensity  of  the  flame  and  the 
speed  of  revolution  of  the  cylinder  may  both  be  regulated.  On 
this  account,  as  well  as  because  the  pieces  of  clinker  are  much 
smaller,  the  cement  is  more  uniformly  burned.  The  remarkable 
development  of  the  Portland  cement  industry  in  the  United 
States  is  due  in  no  small  measure  to  the  adoption  and  perfection 
of  the  rotary  kiln,  for  the  labor  expense  in  manufacture  has  been 
so  reduced  thereby  that  we  are  able  to  successfully  compete 
with  cements  made  abroad  where  lower  wages  prevail. 

28.  GRINDING.  —  In  grinding   it    is   not  sufficient   that  the 
cement  be  so  reduced  that  a  certain  percentage  of  it  will  pass 
a  sieve  having,  say,  10,000  holes  per  square  inch;  but  it  is  de- 
sired  that   as   large  a    proportion  as  possible  shall   be    of   the 
finest  floury   nature.     To   accomplish   this   result   it   has   been 
claimed  that   French   buhr  millstones   are  the  best,  but   their 
great  consumption  of  power  has  led  to  the  introduction  of  other 
forms  of  grinding  machinery,  so  that  at  present  millstones  find 
their  chief  use  in  natural  cement  manufacture.  • 

It  is  usually  considered  that  the  greatest  economy  results 
from  a  gradual  reduction  of  the  clinker  as  it  passes  from  one 
form  of  grinder  to  another,  each  machine  being  supplied  with 
the  size  of  pieces  it  is  best  adapted  to  handle.  Large  pieces  of 
clinker  are  first  passed  through  an  ordinary  rock  crusher,  such 
as  the  Gates  or  Blake.  Where  rotary  kilns  are  in  use,  this  step 
in  the  process  may  be  omitted,  as  the  clinker  comes  from  the 
kiln  in  small,  nut-like  pieces. 

29.  Ball  mills  may  also  be  used  for  the  first  reduction.     The 
ball  mill  is  a  short  cylinder  of  large  diameter  which  is  partially 
filled   with   flint   or  steel   balls.     When   the   cylinder  revolves, 
the  balls  and  the  clinker  fall  upon  hard  metal  surfaces,  and  as 
the   material   is    ground    to   the   size    of   sand    grains,    it   falls 
through  screens   in  the   periphery  into    a  hopper,  where   it  is 
delivered  to  a  conveyor,  or  to  another  form  of    pulverizer  for 
further  reduction. 

30.  Tube  mills  may  be  used  in  connection  with  millstones, 
but  are  usually  employed  for  final  reduction  of  the  product  of 


PORTLAND  CEMENT  21 

the  ball  mill.  The  tube  mill  is  a  steel  cylinder,  about  4  or  5 
feet  in  diameter  and  15  to  25  feet  long,  with  axis  horizontal  or 
nearly  so,  and  revolving  on  trunnions.  The  cylinder  is  lined 
with  hard  iron  or  porcelain,  and  is  half  filled  with  flint  pebbles. 
The  material  is  fed  in  at  one  end  and  is  gradually  pulverized  as 
it  works  toward  the  other  end.  Some  styles  are  not  continuous 
in  their  action,  but  are  charged  and  closed,  the  material  being 
removed  after  a  certain  number  of  revolutions. 

31.  Griffin  Mills.  —  The  Griffin  mill  is  an  American  invention 
that  has  found  much  favor,  especially  in  grinding  tailings  from 
other  mills.     A  heavy  steel  roller  is  attached  to  the  bottom  of  a 
steel  shaft,  which  is  provided  at  its  upper  end  with  a  ball-and- 
socket  joint.     When  the  shaft  is  given  a  gyratory  motion,  the 
roller  presses  by  centrifugal  force  against  the  inside  surface  of  a 
heavy  steel  ring  where  the  grinding  takes  place.     The  material 
which  drops  below  the  roller  is  thrown  up  again  by  steel  blades 
that  are  also  attached  to  the  shaft,  and  when  finally  of  sufficient 
fineness,  the  powder  escapes  through  screens  above  the  ring  into 
a  hopper. 

32.  The  method  of  grinding  to  be  adopted  at  any  mill  de- 
pends upon  the  size  and  hardness  of  the  particles  of  clinker,  but 
usually  the  clinker  is  passed  through  at  least  two  machines. 

It  has  been  stated1  that  the  power  consumed  in  grinding 
one  ton  of  cement  by  the  different  principles  is  as  follows: 

For  millstones      .    .    .    .     30  to  32  I. H. P.  per  ton  per  hour. 

For  ball  principle    ...     16  to  18  I.H.P.        " 

For  edge  runners     ...     12  to  14  I.H.P.        "  " 

The  sifting  of  the  product,  which  formerly  required  special 
revolving  or  shaking  screens  of  wire  cloth,  is  now  usually  done 
by  the  sieves  attached  to  the  grinding  machinery. 

33.  SAND-CEMENT.  —  This  product,  which  is  also  called  silica 
cement,  is  composed  of  Portland  cement  and  silicious  sand  mixed 
in  any  desired  proportion  and  then  ground  to  extreme  fineness. 
This  product  is  placed  on  the  market  by  dealers,  but  rights  to 
use  the  process  may  be  purchased.     In  the  construction  of  Lock 
and  Dam  No.  2,  Mississippi  River,  between  Minneapolis  and 
St.  Paul,  Major  F.  V.  Abbot2  used  the  process,  grinding  with 


1  Mr.  Henry  Faija,  in  Trans.  A.  S.  C.  E.,  Vol.  xxx,  p.  49. 

2  Report  of  Mr.  A.  O.  Powell,  Asst.  Engineer,  Report  Chief  of  Engineers, 
U.  S.  A,,  1900,  p.  2779. 


22  CEMENT  AND  CONCRETE 

a  tube  mill  one  part  of   Portland  cement  with  one  part  fine 
sand.     The  cost,  exclusive  of  plant,  is  estimated  as  follows: 

J  barrel  of  Portland  cement  at  $2.85 $1.42 

I       "    "    sand  at  .05 03 

Cost  of  grinding 50 

Cost  of  royalty 05 

Cost  of  one  barrel  Silica  cement $2.00 

This  cement  has  given  remarkably  high  tests  considering  the 
adulteration  with  sand,  and  is  claimed  to  be  specially  useful  in 
making  impervious  mortar  and  concrete. 

ART.  7.     OTHER  METHODS  OF  MANUFACTURE  OF  PORTLAND 

CEMENT 

34.  Portland  Cement  from  Blast  Furnace  Slag.  —  The  prep- 
aration of  a  true  Portland  cement  from  blast  furnace  slag  has 
been  followed  in  Germany  and  elsewhere  in  Europe  for  several 
years,  and  recently  has  been  introduced  in  the  United   States. 
As  this  process  utilizes  a  waste  product,  its  popularity  is  likely 
to  increase.     Whereas,  for  the  manufacture  of  slag  cement  only 
the  slag  from  gray  pig  iron  is  available,  it  is  found  that  in  most 
cases  the  slag  from  white  pig  iron  may  be  used  for  the  produc- 
tion of  Portland  cement  from  slag. 

The  method  of  manufacture  is  briefly  as  follows:  The  slag 
as  it  comes  from  the  blast  furnace  is  subjected  to  the  action  of 
a  stream  of  water,  which  granulates  it  and  changes  it  chemi- 
cally, the  water  .combining  with  the  calcium  sulphide,  which  is 
injurious  to  cement,  to  form  lime  and  sulphuretted  hydrogen. 
The  granulated  slag  is  then  dried,  mixed  with  the  correct 
proportion  of  dried  limestone,  and  ground  to  extreme  fineness. 
The  mixture  is  next  burned  in  rotary  kilns,  the  remainder  of  the 
process  being  the  same  as  that  employed  when  ordinary  raw 
materials  are  used.  While  a  cement  made  from  slag  by  this 
method  may  have  some  peculiarities  due  to  the  nature  of  the 
raw  materials  used,  and  should  be  very  carefully  tested  before 
it  is  used  in  important  work,  it  should  not  be  confounded  with 
slag  cement,  which  is  a  mixture  of  granulated  slag  and  hydrated 
lime  subsequently  ground,  but  not  burned  together. 

35.  Portland  Cement  from  By-Products  of  Soda  Manufacture. 
—  The  Michigan  Alkali  Company  has  installed  at  Wyandotte, 
Mich.,  a  cement  plant  to  utilize  the  large  amount  of  limestone 


SLAG  CEMENT  23 

which  they  have  as  waste  in  the  manufacture  of  soda  products. 
The  limestone  which  has  served  its  purpose  in  the  soda  manu- 
facture is  in  a  finely  divided  and  semi-fluid  state;  to  this  is 
added  the  proper  percentage  of  clay,  which  has  been  dried  and 
pulverized.  The  two  are  then  very  thoroughly  mixed  by  pug 
mills  and  wash  mills,  the  slurry  corrected  by  small  additions 
of  one  or  the  other  of  the  ingredients,  and  finally  burned  in 
rotary  kilns. 

ART.  8.  THE  MANUFACTURE  OF  SLAG  CEMENT 

36.  Slag  cement  is  made  by  adding  calcium    hydrate  to  a 
granulated  basic  slag  resulting  from  the  manufacture  of  gray 
pig  iron.     The  slag  must  be  carefully  selected  as  to  its  chemical 
composition,  Prof.  Tetmajer  having  found  b^  extended  experi- 
ments that   slags   containing  silica,   alumina,   and  lime  in  the 
ratio  30  to  16  to  40  are  best  adapted  to  the  purpose.     As  the 
molten  slag  runs  from  the  blast  furnace  it  is  suddenly  chilled 
by  being  run  into  water,  or  is  partially  disintegrated  by  being 
treated  with  a  strong  current  of  water,  air,  or  steam.     It  is  thus 
reduced  to  coarse  particles  resembling  sand,  or  to  a  spongy  or 
fibrous  mass  which,  after  drying,  is  readily  ground  to  a  fine 
powder.     The  process  of  chilling  results  in  a  certain  chemico- 
physical  change  that  renders  the  powder  capable  of  combining 
more  readily  with  the  slaked  lime  which  is  subsequently  added. 
Slag  which  has  been  allowed  to  cool  slowly  will  not  form  an 
hydraulic  product  when   mixed   with  the  lime,    although   the 
chemical  composition  of  the  slag  may  be  identical  in  the  two 
cases.     The  lime  is  dipped  into  water,  or  treated  with  steam, 
until  slaked  to  a  fine  dry  powder,  and  is  then  added  to  the 
powdered  slag  in  proportions  of  about  one  part  of  the  former 
to  three  parts  of  the  latter,  this  proportion  depending  upon  the 
composition  of  the  slag  used.     The  powdered  slag  and  lime  are 
sifted,  then  mixed  and  reground  together  to  an  extreme  fine- 
ness, thus  insuring  an  intimate  incorporation  of  the  ingredients. 
Since  there  is  no  burning  in  the  process,  it  is  evident  that  the 
finished  product  is  merely  a  mixture,  not  a  chemical  compound 
as  is  the  case  with  Portland  cement. 

37.  One  of  the  largest  mills  for  the  manufacture  of  slag 
cement  in  the  United  States  is  conducted  by  the  Illinois  Steel 
Company,  and  the  following  description  of  the  process  is  con- 


24  CEMENT  AND  CONCRETE 

densed  from  a  statement  of  Mr.  Jasper  Whiting,1  manager  of 
the  cement  department,  and  patentee  of  the  process:  Slag  of 
the  proper  composition  is  chilled  as  it  comes  from  the  furnace 
by  the  action  of  a  large  stream  of  cold  water  under  high  pres- 
sure. The  slag  is  thereby  broken  up,  about  one-third  of  its 
sulphur  is  eliminated,  and  it  is  otherwise  changed  chemically. 
A  sample  of  the  slag  thus  granulated  is  mixed  with  a  proportion 
of  prepared  lime,  and  ground  in  a  small  mill  whereby  actual 
slag  cement  is  produced.  If  the  tests  upon  this  trial  cement 
are  satisfactory,  the  slag  is  dried  and  then  ground,  first  in  a 
Griffin  mill  and  then  in  a  tube  mill,  where  it  is  mixed  with  the 
proper  amount  of  prepared  lime  and  the  two  materials  ground 
and  intimately  mixed  together.  The  resulting  product  is  said 
to  be  so  fine  that  but  4  per  cent,  is  retained  on  a  sieve  having 
200  meshes  per  linear  inch.  The  lime  is  burned  from  a  very 
pure  limestone  and  stored  in  bins,  beneath  which  are  two 
screens  of  different  mesh,  the  coarser  at  the  top.  A  quantity 
of  lime  being  drawn  on  the  upper  screen  is  slaked  by  the  addi- 
tion of  water  containing  a  small  percentage  of  caustic  soda. 
The  lime  passes  through  the  two  screens  as  it  slakes  and  is 
then  heated  in  a  dryer;  the  slaking  being  thus  completed,  the 
lime  may  be  incorporated  with  the  slag.  The  purpose  of  the 
caustic  soda  added  in  the  above  process  is  to  render  the  cement 
quicker  setting. 

ART.  9.   THE  MANUFACTURE  OF  NATURAL  CEMENT 

38.  History.  —  The  American  product  called  natural  cement 
was    first    manufactured    at    Fayetteville,    Onondaga    County, 
N.  Y.,  in  1818,  and  used  in  the  construction  of  the  Erie  Canal. 
Other  early  dates  of  manufacture  are  given  as  1823,  near  Rosen- 
dale,  N.  Y.,  and  1824  at  Williamsville,  Erie  County,  N.Y.,  the 
products  being  used  in  the  construction  of  the  Erie  and  the 
Delaware  &  Hudson  Canals.      Factories  were    soon   started   in 
other  states,  and  at  present  nearly  every  State  in  the  Union  has 
one  or  more  natural  cement  factories,  the  total  annual  produc- 
tion being  now  about  nine  million  barrels. 

39.  Materials    Required.  —  The    composition    of    rock   from 
which  natural  cement  may  be  made,  varies  within  wide  limits. 
As  stated  in  §13,  an  argillaceous  limestone,  a  magnesian  lime- 


1  "  Report  of  Board  of  Engineers  on  Steel  Portland  Cement,"  Appendix  I. 


•  NATURAL  CEMENT  25 

stone  or  an  argillo-magnesian  limestone  may  be  used.  Argilla- 
ceous limestone  makes  what  is  sometimes  called  an  aluminous 
natural  cement,  its  essential  ingredient  being  a  bisilicate,  or  sili- 
cate of  alumina  and  lime,  while  the  product  made  from  mag- 
nesian  limestone  is  called  magnesian  cement  and  is  composed 
of  a  triple  silicate  of  lime,  magnesia  and  alumina. 

The  Maryland  cements  are  typical  of  the  former  or  alumi- 
nous variety,  containing  only  one  to  five  per  cent,  of  magnesia, 
while  the  Rosendale  and  the  Milwaukee  are  magnesian  cements 
containing  15  to  25  per  cent,  magnesia.  (See  Table  3.) 

With  a  given  raw  material,  the  silica  and  alumina  should 
bear  a  certain  proportion  to  the  lime  and  magnesia,  but  close 
limits  cannot  be  stated  for  this  proportion,  as  it  varies  with  the 
chemical  and  physical  character  of  the  rock.  The  silica  should 
be  combined  with  the  alumina,  not  in  the  form  of  sand. 

The  materials  found  at  any  locality  may  vary  considerably 
as  to  chemical  composition,  especially  among  the  several  strata. 
In  some  cases  the  different  strata'  are  utilized  to  make  two  or 
more  brands,  which  differ  somewhat  in  their  characteristics  as 
to  time  of  setting,  etc.  It  is  common  also  to  mix  two  or  more 
layers  together  in  the  manufacture,  with  the  idea  that  the  in- 
gredients lacking  in  one  stratum  will  be  supplied  by  the  others. 

40.  DESCRIPTION  OF  PROCESS.  —  As  the  proper  ingredients 
to  produce  the  cement  have  been  incorporated  by  Nature,  that 
part  of  the  process  of  Portland  cement  manufacture  preliminary 
to  the  burning  is  unnecessary.  The  rock  occurs  in  strata  and  is 
either  quarried  in  open  cut  where  the  stripping  is  light,  or  by 
means  of  tunnels.  In  open  cut,  a  face  of  twenty  feet  or  more  is 
sometimes  worked.  As  has  already  been  stated,  the  strata  vary 
in  chemical  composition,  and  while  two  or  more  brands  are 
sometimes  made  at  the  same  mill,  it  is  a  more  general  practice 
to  mix  the  rock  from  several  strata  in  the  production  of  one 
brand.  The  idea  is  that  if  one  layer  contains  too  much  silica,  it 
may  be  corrected  by  another  containing  too  much  lime  or  mag- 
nesia. As  the  rock  is  not  finely  pulverized  before  it  enters  the 
kiln,  each  lump  burns  by  itself  and  makes  a  certain  cement;  the 
piece  of  rock  next  it  must  make  as  distinct  a  product  as  though 
burned  in  a  separate  kiln.  What  is  obtained,  then,  by  this 
method  is  a  mixture  of  several  cements,  and  it  is  questionable 
whether  the  mere  mechanical  mixing  of  an  over-limed  cement 


26  CEMENT  AND  CONCRETE 

with  an  over- clayed  one  will  make  a  well  balanced  product. 
This  practice  may  account,  in  a  great  degree,  for  the  large  vari- 
ations that  occur  in  the  cement  from  a  single  factory,  variations 
which  are  often,  however,  more  noticeable  in  short-time  tests 
than  in  the  longer  ones. 

41.  The  rock,  as   quarried,  is   broken   by  an   ordinary  rock 
crusher  or  otherwise,  into  pieces  varying  in  size  up  to  six  inches, 
and  is  then  conveyed,  usually  by  tramway,  directly  to  the  kilns. 
These  are  of  the  cylindrical  continuous  type,  built  of  stone  or 
steel,  and  lined  with  fire  brick.     The  kilns  are  commonly  about 
45  feet  high  and  16  feet  in  diameter;  the  tramway  leads  to  a 
loading  platform  on  top  of  the  kiln.     According  to  the  locality, 
the  fuel  may  be  either  bituminous  or  anthracite  coal  of  about 
pea  size.     The  rock  and  fuel  are  spread  in  the  top  of  the  kiln  in 
alternating  layers,  the  proportion  of  fuel  being  usually  regulated 
by  the  man  in  charge  of  the  burning,  but  sometimes  a  machine 
is  employed  which  automatically  governs  the  amount  of  coal 
used.     The  temperature  in  the  kilns  is  much  below  that  required 
in   Portland    cement    manufacture,  but  varies    of    course    with 
the  materials. 

42.  The  calcined  rock  is  conveyed  first  to  some  sort  of  a 
stone  crusher;  a  common  form  is  known  as  a  "  pot-cracker/7  and 
consists  of  a  corrugated  conical  shell  in  which  works  a  cast  iron 
core,  also  corrugated.     After  passing  the  cracker,  the  material 
may  be  screened,  giving  a  certain  proportion  of  finished  product, 
and   another  portion  which   may  go   directly   to   the   finishing 
stones,  while  the  coarsest  pieces  are  conveyed  to  another  form 
of  cracker,  such  as  iron  edge  runners,  which  prepares  it  for  the 
millstones.     In   many   factories   ordinary   under-run   millstones 
are  used,  in  others  rock  emery  stones  are  employed,  while  in 
some  factories  stones  found   locally  prove  satisfactory.     There 
have  been  recently  installed  in  some  of  the  natural  cement  fac- 
tories, ball  and  tube   mills  for  grinding  as  used  for  Portland 
cement  clinker,  and  in  several  factories  special  forms  of  grinding 
machinery  are  in  use  that  have  been  perfected  by  the  managers 
of  the  works. 

The  product  passes  from  the  reducing  mills  *to  the  "  mixers," 
by  means  of  which  the  material  is  thoroughly  mixed  to  promote 
uniformity.  It  is  now  ready  for  packing,  and  may  be  conveyed 
directly  to  the  chute  from  which  the  barrels  or  bags  are  filled. 


NATURAL  CEMENT  27 

In  packing,  the  barrel  rests  upon  a  circular  disc  which  is  given 
a  vertical  jarring  motion,  and  thus  the  cement  is  thoroughly 
settled  in  the  barrel. 

It  is  seen  that  the  manufacture  of  natural  cement  is  very 
similar  to  that  portion  of  Portland  cement  manufacture  suc- 
ceeding the  preparation  of  the  raw  material  for  burning.  In 
general,  less  care  is  requisite  with  natural  cement,  the  burning 
is  carried  on  at  a  lower  temperature,  and  the  calcined  rock  is 
softer,  so  that  less  expense  is  incurred  in  grinding. 


PART  II 

THE    PROPERTIES    OF    CEMENT   AND 
METHODS    OF   TESTING 


CHAPTER  III 

INTRODUCTORY 

43.  In  the  tests  of  such  structural  materials  as  wood  and 
steel  it  will  not  usually  be  difficult  to  determine  the  suitability 
of   the   material   for   the  intended   purpose,   provided   the   test 
pieces  truthfully  represent  the  members  to  be  used.     It  is  known 
that  so  long  as  these  members  are  protected  from  oxidation  and 
over-loading  they  will  retain  their  qualities,  and  there  is  always 
a  reasonably  clear  understanding  of  what  these  qualities  should 
be.     On  the  other  hand,  in  the  testing  of  cement,  one  may  be 
perfectly  sure  that  from  the  moment  the  cement  is  manufac- 
tured until  long  after  it  has  been  in  service  in  the  structure  its 
properties   will   be   ever   changing;   and,   further,   the   qualities 
which  it  is  desirable  the  cement  should  possess  are  not  always 
clearly  in  mind. 

44.  Desirable  Qualities  in  Cement.  —  The  desirable  elements 
in  a  cement  may  be  stated  as  follows:  1st,  That  when  treated  in 
the  propo&ed  manner  it  shall  develop  a  certain  strength  at  the 
end  of  a  given  period.     2d,  That  it  shall  contain  no  compounds 
within  itself  which  may,  at  any  future  time,  cause  it  to  change 
its  form  or  volume,  or  lose  any  of  its  previously  acquired  strength. 
3d,  That  it  shall  be  able  to  withstand  the  action  of  any  exterior 
agency  to  which  it  may  be  subjected  that  would  tend  to  decrease 
its 'strength  or  change  its  form  or  volume.     When  it  is  deter- 
mined that  a  cement  has  these  three  qualities,  it  is  certain  that 
it  is  safe  to  use  it,  but  it  is  further  desirable  to  know  that  the 


UNIFORM   METHODS  29 

cement  in  question  will  accomplish  the  given  object  as  cheaply 
as  any  other  cement. 

The  cohesive  and  adhesive  strengths  of  cement  are  not  usu- 
ally considered  in  the  design  of  the  structure  into  which  cement 
enters.  The  design  of  a  masonry  arch  does  not  comprehend  any 
adhesive  strength  in  the  cement,  except  as  it  may  be  recognized 
as  an  additional  factor  of  safety,  and  a  masonry  dam  is  so  de- 
signed that  there  shall  be  no  tension  at  the  heel.  These  facts 
are  due  in  a  large  measure  to  the  very  imperfect  knowledge  we 
have  of  the  behavior  of  cements  in  various  contingencies.  With 
the  increasing  use  of  concrete,  as  in  arches,  locks,  floors,  roofs, 
etc.,  the  tensile  and  transverse  strengths  of  cement  are  coming 
to  be  relied  on  to  a  certain  extent;  and  as  its  properties  become 
better  known,  and  as  means  of  recognizing  these  properties 
become  more  certain  and  widespread  in  their  application,  ce- 
ment will  be  more  extensively  employed  in  a  scientific  and  eco- 
nomical manner. 

Cement  may  be  compared  in  one  sense  to  timber  and  cast 
iron.  A  large  factor  of  safety  is  employed  when  dealing  with 
these  materials  because  of  hidden  defects  that  may  exist.  The 
defects  which  lie  hidden  in  cement  may  be  even  greater  than 
these  in  proportion  to  its  possible  strength,  and  defects  in  ce- 
ment are  often  more  treacherous  because  their  development 
may  be  deferred  for  some  time.  The  importance  of  knowing 
whether  the  cement  fulfills  the  second  and  third  requirements 
noted  above  is  therefore  evident. 

45.  Having  considered  the  qualities  a  cement  should  have, 
we  may  proceed  to  the  detailed  consideration  of  the  various 
tests  employed  to  disclose  the  presence  or  absence  of  these  qual- 
ifies. The  strength  a  given  cement  will  develop  is  investigated 
by  chemical  analysis,  by  obtaining  the  specific  gravity  and  fine- 
ness, and  by  actual  rupture  tests,  whether  they  be  tensile,  com- 
pressive,  transverse,  or  shearing.  By  tests  for  change  of  volume 
and  by  chemical  analysis,  it  is  sought  to  determine  whether  a 
cement  has  within  itself  elements  of  destruction.  For  the  power 
to  withstand  external  agencies  there  are  no  adequate  tests, 
though  chemical  analysis  is  considered  an  aid.  The  methods 
of  use,  the  proportions  of  the  materials,  their  incorporation  and 
deposition  are  of  great  importance  in  insuring  against  external 
causes  of  injury. 


30  CEMENT  AND  CONCRETE 

46.  Uniform  Methods  of  Cement  Testing.  —  In  order  that 
uniformity  should  prevail  in  the  methods  employed  in  testing 
cements,  various  societies  have  discussed  the  subject  in  detail, 
usually  through  committees,  and  much  valuable  work  has  been 
done  along  this  line.     The  engineers  of  public  works  in  many 
European  countries  have  adopted  specifications  and  laid  down 
more  or  less  detailed  rules  for  testing.     The  Corps  of  Engineers, 
U.  S.  A.,  has  recently  adopted  a  similar  code  of  rules. 

The  International  Society  for  Testing  Materials,  with  which 
the  American  Society  for  Testing  Materials  is  affiliated,  has  con- 
sidered the  subject  and  still  has  committees  at  work  upon  it. 
The  New  York  section  of  the  Society  of  Chemical  Industry  has 
recently  formulated  a  method  for  analysis  of  materials  for  the 
Portland  cement  industry.  The  American  Society  of  Civil  En- 
gineers received  a  report  in  1885  from  a  committee  appointed 
to  consider  methods  of  cement  testing,  and  in  order  to  keep  the 
subject  abreast  of  the  latest  developments  in  the  manufacture 
and  use  of  cement,  a  second  committee  was  appointed  several 
years  ago,  which  has  been  making  a  thorough  discussion  of  the 
subject,  and  has  submitted  a  preliminary  or  progress  report. 

47.  Notwithstanding  that  so  much   has  been  done  toward 
unification  of  methods,  it  may  never  be  possible  to  determine 
accurately  the  value  of  one  cement  as  compared  with  another 
tested  in  a  different  laboratory;  though  in  tests  of  iron  and 
steel  no  such  difficulty  is  experienced.     Certainly,  as  at  present 
carried  out,  strength  tests  of  cement  are  purely  relative  tests 
and  do  not  show  the  absolute  strength  which  may  be  developed 
in  the  structures;  nor  can  the  results  be  compared  with  the  re- 
sults obtained  in  other  laboratories  and  any  fine  distinctions  of 
quality  drawn.     To  attempt  to  carry  out  acceptance  tests  fti 
such  a  way  as  to  show  directly  the  strength  which  will  be  de- 
veloped in  actual  construction,  is  only  to  introduce  causes  of 
irregularity  in  the  tests. 


CHAPTER  IV 

CHEMICAL   TESTS 

ART.  10.    COMPOSITION  AND  CHEMICAL  ANALYSIS 

48.  Value  of  Chemical  Tests.  —  The  definite  aid  which  chem- 
ical analysis  may  render  in  determining  the  quality  of  a  cement 
is  limited  by  the  following  considerations.     It  is  not  definitely 
known  just  what  part  is  played  by  each  of  the  compounds  that 
go  to  make  up  commercial  cement,  and  chemical  analysis  does 
not  tell  the  manner  of  the  occurrence  of  these  compounds.     A 
cement  may  have  a  chemical  composition  that  is  thought  to  be 
perfect,  but  if  the  burning  has  not  been  properly  accomplished, 
it  may  be  a  dangerous  product  and  analysis  would  show  no  de- 
fect.    Some  of  the  best  authorities  say  that  chemical  analysis 
is  useful  principally  in  tracing  the  cause  of  defects  which,  by 
other  tests,  have  been  found  to  exist.     However,  there  are  some 
constituents  which  it  is  fairly  well  known  a  cement  should  not 
contain  in  any  considerable  quantities.     An  analysis  may  be  of 
value  in  estimating  quantitatively  such  constituents,  while  it 
may  also  be  of  service  in  detecting  adulterations.     It  is  not  im- 
possible, then,  that  chemical  tests  may  yet  play  a  more  impor- 
tant role  in  cement  testing,  especially  if  the  method  of  analysis 
can  be  made  more  simple  and  rapid,  without  too  great  a  sacri- 
fice of  accuracy. 

49.  Lime.  —  The  proportion  of  lime  in  Portland  cement  may 
vary  from  59  to  67  per  cent.     A  much  greater  range  than  this 
is  allowable  in  natural  cement,  the  percentage  usually  being 
from  30  to  45,  according  to  the  amount  and   character  of  the 
other  active  constituents.     An  analysis  of  Portland  cement  which 
shows  a  percentage  of  lime  far  outside  of  the  limits  mentioned 
above,  should  be  regarded  with  suspicion  and  submitted  to  very 
thorough  tests  before  acceptance.     As  already  stated,  the  ratio 
of  the  silica  and  alumina  to  the  lime  in  a  cement  is  called  the 
hydraulic  index.     The  value  of  this  ratio  is  usually  between  .42 
and  .48  for  Portland  cement. 

31 


32  CEMENT  AND  CONCRETE 

Cement  mixtures  containing  a  large  percentage  of  lime  re- 
quire a  high  temperature  for  calcination,  are  difficult  to  grind, 
and  yield  a  slow-setting  product.  The  danger  in  highly  limed 
cements  is  that  they  will  not  be  properly  calcined  and  a  por- 
tion of  the  lime  will  be  left  in  a  free  state.  The  demand  for 
high  strength  in  short-time  tests  has  led  manufacturers  to 
make  a  heavily  limed  product,  and  in  some  cases  the  limits  of 
safety  have  probably  been  overstepped.  The  introduction  of  the 
rotary  kiln,  however,  has  so  improved  the  facilities  for  burning 
cement  that  a  higher  percentage  of  lime  is  now  possible. 

There  is  no  method  known  at  present  for  determining  quanti- 
tatively the  amount  of  free  lime  in  a  cement,  and  it  seems  doubt- 
ful whether  its  presence  can  be  detected  with  certainty  by  chemi- 
cal analysis.  The  method  usually  employed  for  this  purpose 
depends  on  the  hydration  of  the  lime  and  subsequent  absorption 
of  carbonic  acid. 

50.  Magnesia.  —  The  detection  of  magnesia  in  several  con- 
crete structures  that  had  failed,  led  to  the  conclusion  that  mag- 
nesia, in  quantities  exceeding  two  or  three  per  cent.,  was  a 
dangerous  element  in  Portland  cement.  In  1886-87  Mr.  Har- 
rison Hayter1  mentioned  several  failures  of  masonry  and  con- 
crete which  he  considered  were  due  to  magnesia,  and  concluded 
that  cemerut  should  not  contain  more  than  one  per  cent.  Later 
investigations,  however,  indicated  that  such  failures  could  be 
explained  in  other  ways,  and  that  the  magnesia  found  in  the 
failing  structure  had  come  from  the  sea  water  and  replaced  the 
lime  in  the  cement.  Mr.  A.  E.  Carey2  has  considered  that  "an 
excess  of  caustic  lime  or  magnesia  causes  first,  disintegration 
by  expansion  due  to  hydration,  and  second,  being  soluble,  when 
conditions  permit  of  their  washing  out,  leave  the  concrete  in  a 
honeycombed  state."  Notice  that  this  refers  to  caustic  mag- 
nesia, and  Prof.  S.  B.  Newberry3  has  stated  that  "it  is  doubtful 
if  magnesia  is  ever  combined  in  Portland  cement.  Our  own 
experiments  tend  to  confirm  the  opinion  of  many  German 
authorities  that  magnesia  remains  free  in  cement  and  does 
not  combine  with  the  constituents  of  clay  after  the  manner 
of  lime." 


1  Proc.  Inst.  C.  E.,  Part  1,  Session  of  1886-87. 

2  Ibid.,  1891-92. 

3  Municipal  Engineering,  October,  1896. 


COMPOSITION  AND  ANALYSIS  33 

On  the  other  hand,  M.  H.  LeChatelier  l  says  that  the  ''acci- 
dents occasioned  by  certain  magnesian  elements,  and  the  similar 
results  obtained  in  laboratory  experiments,  have  been  due  to 
the  employment  of  badly  proportioned  cements,  containing  free 
uncombined  magnesia  and  too  small  a  quantity  of  clay.  Cor- 
responding mixtures  containing  lime  instead  of  magnesia  would 
have  caused  still  more  serious  accidents,  yet  it  would  not  be  con- 
cluded that  there  must  be  no  lime  in  cement."  Again,  Dr. 
Erdmenger  characterizes  magnesia  as  an  adulterant  only,  and 
considers  that  its  effect  is  nil  if  a  greater  percentage  of  lime  is 
added  in  the  manufacture. 

Some  authoritative  information  on  the  amount  of  magnesia 
allowable  in  Portland  cement  is  contained  in  the  report  of  the 
magnesia  commission  of  the  Association  of  German  Cement 
Makers,  1895:  Three  members  of  this  committee,  Messrs.  Schott, 
Meyer  and  Arendt  concluded  that  "the  presence  of  magnesia 
up  to  ten  per  cent,  causes  no  harmful  expansion  or  cracking  of 
the  cement,  even  after  several  years."  Mr.  Dyckerhoff,  how- 
ever, presented  a  minority  report,  in  which  he  pointed  out  that 
while  a  large  amount  of  magnesia,  not  sintered,  may  not  have 
an  injurious  effect,  yet  a  content  of  more  than  four  per  cent,  of 
sintered  magnesia,  whether  added  or  substituted  for  part  of  the 
lime,  has  an  injurious  effect  after  long  periods.  The  committee 
continued  the  ruling  of  1893  that  "a  magnesia  content  of  five 
per  cent,  in  burnt  cement  is  harmless,"  but  held  the  question 
open  for  further  investigation,  indicating  that  this  limit  might 
be  raised. 

In  view  of  the  disagreement  among  such  eminent  authori- 
ties it  is  impossible  to  arrive  at  a  satisfactory  conclusion,  but  if 
the  effect  of  magnesia  depends  upon  the  manner  of  its  occur- 
rence, whether  free  or  combined,  sintered  or  unsintered,  then 
chemical  analysis  can  be  of  but  limited  value  as  a  test  of  quality 
in  this  regard.  Natural  cements  frequently  contain  large  pro- 
portions of  magnesia  replacing  lime,  and  in  this  case  an  analysis 
is  of  the  same  value  as  an  analysis  for  lime. 

51.  Alumina  and  Iron  Oxide.  —  The  amount  of  alumina 
which  a  cement  should  contain  is  not  well  established.  Its 
presence  tends  to  facilitate  the  burning,  and  it  renders  the  prod- 


1  Trans.  Amer.  Inst.  Mining  Engrs.,  1893. 


34  CEMENT  AND  CONCRETE 

uct  quicker  setting.  Cements  containing  large  percentages  of 
alumina  are  inferior  for  use  in  air  or  sea  water,  and  it  is  probable 
that  the  percentage  of  alumina  should  not  exceed  eight  or  ten 
to  obtain  the  best  results  in  all  media.  A  slag  cement  may  be 
detected  by  its  large  content  of  alumina.  Oxide  of  iron  acts 
as  a  flux  in  burning,  but  in  the  finished  product  is  little  more 
than  an  adulterant. 

52.  Sulphuric  Acid.  —  French  specifications  say  that  Port- 
land cements  shall  not  contain  more  than  one  per  cent,  of  sul- 
phuric acid  or  sulphides  in  determinable  proportions.     This  is 
doubtless  intended  for  cement  to  be  used  in  sea  water.     Adul- 
terations with  blast-furnace  slag  may  sometimes  be  detected 
by  the  amount  of  sulphides  present,  but  small  quantities  of  sul- 
phuric acid  in  the  cement  may  be  derived  from  the  coke  used 
in  burning  and  have  no  injurious  effect  for  use  in  fresh  water. 
A  content  of  1.75  per  cent,  of  sulphuric  anhydride,  S08,  is  now  con- 
sidered  the  maximum  permissible.     Sulphates  mixed   with  the 
raw  materials  and   burned  with  the  cement  may  be  harmless, 
while  the  same  amount  added  after  burning  would  not  be  per- 
missible.    [For  tests  on  the  effect  of  adding  sulphate  of  lime  to 
cement,  see  Art.  48.] 

53.  Water  and  Carbonic  Acid.  —  The  determination  of  these 
may  give  some  idea  of  the  deterioration  of  a  product  by  storage, 
and  they  may  also  indicate  defective  burning.     M.  Candlot  con- 
siders that  in  the  case  of  Portland  cement,  a  loss  on  ignition 
(water  and  carbon  dioxide)  exceeding  three  per  cent.  " indicates 
that  the  cement  has  undergone  sufficient  alteration  to  appre- 
ciably diminish  its  strength."     Natural  cements  may,  however, 
contain  considerable  proportions  of  these  ingredients  and  still 
give  good  results. 

54.  Conclusions.  —  Finally,  then,  the  determination  of  silica, 
alumina,  magnesia  and  lime  may  be  of  value,  first,  in  classify- 
ing a  product,  and  second,  as  indicating  whether  the  proportions 
contained  in  it  are  such  that  if  properly  manufactured  it  is 
capable  of  giving  good  results.     What  these  proportions  should 
be  for  Portland  cement  has  already  been  stated,  §  9.     The  de- 
termination  of   certain   injurious   ingredients   is   also    of   some 
value,  but  it  must  be  remembered  that  the  dangerous  elements 
most  commonly  occurring,  namely,  free  lime  and  magnesia,  are 
not  determinable  by  chemical  analysis.     It  has  been  stated  by 


COMPOSITION  AND  ANALYSIS  35 

M.  LeChatelier  that  "  neither  complete  nor  partial  chemical 
analysis  of  the  constituents  of  hydraulic  materials  can  be  ranked 
among  normal  tests.  But  chemical  analysis  may  render  real 
service  in  controlling  the  classification  of  a  product  concerning 
which  there  is  reason  to  doubt  the  declaration  of  the  manufac- 
turer. Thus,  a  slag  cement  can  be  distinguished  from  a  Port- 
land by  its  tenor  in  alumina  and  water;  certain  natural  cements, 
by  their  contents  of  sulphuric  acid,  etc."  l 

The  methods  of  analysis  for  Portland  cement  are  given  in 
considerable  detail  in  a  little  book,  "  The  Chemical  and  Physical 
Examination  of  Portland  Cement,"  by  Richard  K.  Meade.  The 
method  of  analysis  suggested  by  the  New  York  Section  of  the 
Society  of  Chemical  Industry  is  published  in  the  Engineering 
Record  of  July  11,  1903,  and  in  Engineering  News  of  July  16, 
1903. 


"Tests  of  Hydraulic  Materials/'  H.  LeChatelier. 


CHAPTER  V 

THE   SIMPLER   PHYSICAL  TESTS 
ART.   11.    MICROSCOPICAL  TESTS.     COLOR 

55.  Microscopical   examinations    are    of   some    interest    and 
value  to  those  who  are  thoroughly  versed  in  the  chemistry  of 
the  burning  and  hardening  of  cements,  as  an  aid  in  determining 
the  part  played  by  each  compound  in  the  hardening. 

Examinations  may  be  made  either  of  the  dry  powder,  or  of 
thin  sections  of  hardened  cement,  or  clinker.  Dry  powder  of 
Portland  cement  appears  to  be  made  up  of  scaly  particles,  many 
of  which  are  clearly  defined  and  semi-transparent,  while  natural 
cement  particles  are  more  nearly  opaque  and  less  angular.  Thin 
sections  of  Portland  cement  clinker  have  been  found  to  exhibit 
colorless  crystals  somewhat  cubical  in  structure,  which  are 
thought  to  form  the  essential  hardening  constituent;  thin  sec- 
tions of  hardened  Portland  cement  show  a  clear  crystalline 
structure.  Prof.  Hayter  Lewis  found  that  the  particles  in  good 
Portland  cement  were  angular  in  form,  consisting  of  scales  and 
splinters,  while  the  particles  of  cement  of  poor  quality  were 
rounded  or  nodular. 

Microscopic  examinations  have  no  place  at  present  in  ordi- 
nary tests  of  quality. 

56.  Significance  of  Color.  —  The  color  of  cement  is  chiefly 
derived  from  its  impurities,  such  as  oxides  of  iron  and  manga- 
nese, rather  than  from  its  essential  ingredients,  and  the  color  is 
therefore  of  minor  importance.     Other  things  being  equal,   a 
hard  burned  Portland  cement  will  be  darker  in  color  than  an 
underburned  product.     An  excess  of  lime  may  be  indicated  by 
a  bluish  cast,  and  excess  of  clay  or  underburning  may  give  a 
brownish  shade.     Gray  or  greenish  gray  is  usually  considered 
to  be  indicative  of  a  good  Portland. 

57.  The  colors  of  natural  cements  have  a  wide  range,  vary- 
ing from  a  light  yellow  to  a  very  dark  brown,  without  reference 
to  quality.     Owing  to  a  popular  idea  that  dark  color  indicated 


WEIGHT  PER   CUBIC  FOOT  37 

strength,  some  manufacturers  have  been  said  to  add  coloring 
matter  to  their  product,  but  although  this  may  have  been  true 
at  one  time,  the  correction  of  this  false  idea  has  doubtless  ren- 
dered such  a  practice  quite  unnecessary  now.  Variations  in 
shade  in  different  samples  of  the  same  brand  of  natural  cement 
may  indicate  differences  in  burning  or  in  the  composition  of  the 
rock;  but  the  interpretation  of  color  for  any  given  brand  must 
be  the  result  of  close  study,  for  some  cements  become  lighter 
on  burning  and  others  become  darker,  while  in  some  cases  no 
variation  in  shade  can  be  detected  for  different  degrees  of 
burning. 

ART.  12.     WEIGHT  PER  CUBIC  FOOT  OR  APPARENT  DENSITY 

58.  Significance.  —  Since   a   hard    burned   Portland   cement 
will  usually  be  heavier  than  a  light  burned  one,  a  test  of  the 
weight  per  cubic  foot  was  once  thought  to  be  of  great  value  in 
judging  of  the  degree  of  burning.     But  it  has  been  shown  re- 
peatedly that  the  weight  per  cubic  foot  depends  quite  as  much 
on  the  fineness  as  on  the  burning.     It  also  depends  on  the  age 
of  the  cement,  and  its  chemical  composition.     As  a  test  for 
quality,  the  determination  of  the  apparent  density  has  therefore 
been  discarded.     However,  it  is  an  aid  in  classifying  a  product, 
since  Portland  cements  weigh  from  70  to  90  pounds  per  cubic 
foot  when  loosely  filled  in  a  measure,  while  natural  cements 
weigh  from  45  to  65  pounds.     A  knowledge  of  the  weight  per 
cubic  foot  is  also  useful  in  reducing  proportions  given  by  weight 
to  equivalent  volumetric  proportions,  and  vice  versa. 

59.  Method.  —  This   test  may  be  made  with  a  very  simple 
apparatus,  and  the  results  obtained,  though  not  strictly  accu- 
rate, are  sufficient  for  all  practical  purposes.     A  metal  tube, 

2  feet  4  inches  long,  about  6  inches  in  diameter  at  the  top,  and 

3  or  4  inches  at  the  bottom,  is  supported  by  a  frame  resting  on 
four  legs.     A  metal   cylinder,   6  inches  in  diameter  and   6j\ 
inches  deep,  holding  one-tenth  cubic  foot,  is  placed  on  the  floor 
below  the  tube.     A  coarse  sieve,  through  which  all  of  the  ce- 
ment will  pass,  is  placed  on  top  of  the  tube  and  three  fe.et  above 
the  bottom  of  the  measure.     The  cement  passes  through  the 
sieve,  falling  freely  to  the  cylinder  below,  which  is  struck  off 
level  when  full.     The  cement  must  not  be  heaped  too  much, 
and  great  care  must  be  taken  that  the  measure  is  not  jarred 


38  CEMENT  AND  CONCRETE 

while  it  is  being  filled  or  struck  off.  The  cement  is  in  such  a 
light  condition  that  a  very  slight  jar  is  sufficient  to  cause  it  to 
settle. 

The  above  apparatus  is  on  the  same  plan  as  that  used  by 
Mr.  E.  C.  Clarke  on  the  Boston  Main  Drainage  Works,  and  is 
described  here  for  general  use  when  it  is  desired  to  compare 
the  results  obtained  by  operators  at  different  points.  Should 
one  wish  simply  to  obtain  a  series  of  results  on  different  cements 
which  are  to  be  compared  among  themselves,  it  is  quite  suf- 
ficient to  sift  each  sample  through  a  coarse  sieve,  and  then  with 
an  ordinary  scoop  carefully  fill  a  measure  of  any  known  capac- 
ity, without  other  apparatus. 

Mr.  Henry  Faija  has  described  an  apparatus  consisting  of  a 
funnel  with  a  screw  at  the  mouth  which  carries  the  cement 
horizontally  to  the  point  where  it  falls  freely  into  the  measure. 
Various  other  devices  have  been  employed,  but  none  seems  to 
have  met  with  universal  favor. 

60.  To  determine  the  relative  accuracy  obtainable  with  the 
simple  form  of  apparatus  first  described,  the  author  made  a 
series  of  tests  which  may  be  summarized  as  follows :  — 

1st  Method.  —  Cement  passed  a  wire  mesh  sieve,  holes  .033 
inch  square  and  fell  freely  two  feet  through  a  6-inch  tube  into 
a  measure  holding  J  cu.  ft.  Five  trials  with  a  sample  of  Dycker- 
hoff  Portland,  highest  weight  per  cubic  foot,  81  Ibs.  4  oz., 
lowest,  79  Ibs.  2  oz.,  difference,  2  Ibs.  2  oz.  Three  trials  with 
Alsen's  Portland,  highest  weight,  73  Ibs.,  lowest,  72  Ibs.,  dif- 
ference, 1  Ib. 

2d  Method.  —  Measure  same  size  filled  with  scoop  without 
other  apparatus,  and  cement  not  shaken  or  jarred  in  measure. 
Five  trials  with  Alsen's  Portland,  highest  result,  73  Ibs.  8  oz. 
per  cu.  ft.,  lowest  result,  72  Ibs.  12  oz.,  difference,  12  oz.  Five 
trials  with  different  sample  of  same  cement,  highest,  72  Ibs. 
4  oz.,  lowest,  72  Ibs.,  difference,  4  oz. 

3d  Method.  —  Measure  filled  with  scoop,  and  cement  well 
shaken  down  as  filling  proceeded.  Five  trials  with  Alsen's 
Portland,  highest  result,  100  Ibs.  8  oz.,  lowest,  97  Ibs.  14  oz., 
difference,  2  Ibs.  10  oz. 

It  appears  from  these  tests  that  when  the  measure  is  filled 
with  the  scoop,  the  results  are  about  as  uniform  as  when  the 
apparatus  is  used,  provided  the  filling  is  always  done  by  the 


SPECIFIC  GRAVITY  39 

same  person.  But  the  results  obtained  by  different  operators 
with  the  same  sample  of  cement  would  probably  vary  less,  one 
from  the  other,  when  the  apparatus  is  employed.  In  other 
words,  the  personal  factor  is  more  nearly  eliminated  when  the 
cement  is  passed  through  a  sieve  and  allowed  to  fall  freely 
from  a  given  height. 

61.  As  to  the  effect  of   age  on  the  weight  per  cubic  foot,  it 
was  found  in  one  case  that  cement  which  weighed  93^  pounds 
per   cubic   foot   when   freshly  ground,  weighed   but   88  pounds 
when  a  few  days  old,  and  78  and  74  pounds  after  six  months 
and  one  year,  respectively.1 

Many  experiments  have  been  made  to  show  the  effect  of 
fineness  on  the  weight  per  cubic  foot,  but  as  this  subject  will 
be  taken  up  again  under  "fineness,"  it  will  suffice  to  quote  one 
series  of  tests  made  by  Mr.  E.  C.  Clarke,2  giving  the  "  weight 
per  cubic  foot  of  the  same  sample  of  German  Portland  cement 
containing  different  percentages  of  coarse  particles  as  deter- 
mined by  sifting  through  the  No.  120  sieve." 

Samples  containing  0,  10,  20,  30,  and  40  per  cent,  of  coarse 
particles  retained  on  No.  120  sieve  gave  the  following  weights 
per  cubic  foot:  75,  79,  82,  86  and  90  pounds,  respectively. 

It  may  be  repeated  that  the  weight  per  cubic  foot  is  no 
longer  considered  an  indication  of  quality,  but  should  it  be 
desired  to  specify  a  given  weight,  the  method  by  which  the 
test  is  to  be  made  should  also  be  stated. 

ART.   13.     SPECIFIC  GRAVITY  OR  TRUE  DENSITY 

62.  The  apparent   density  or  weight  per  cubic  foot  is  in- 
fluenced to  such  an  extent  by  the  degree  of  fineness  of  the 
cement  that  this  test  has  been  almost  superseded  by  the  test 
for   specific   gravity.     Although   the    true   density,    or   specific 
gravity,  is  not  affected  by  the  fineness,  it  is  influenced  by  the 
composition,  the  degree  of  burning,  and  the  age,  or  amount  of 
aeration  of  the  sample. 

The  method  commonly  employed  in  this  test  consists  in  de- 
termining the  absolute  volume  of  a  given  weight  of  the  cement 


"Cement  for  Users,"  by  H.  Faija,  p.  54. 

2  "  Record  of  Tests  of  Cements  for  Boston  Main  Drainage  Works,"  Trans. 
A.  S.  C.  E.,  Vol.  xiv,  p.  144. 


40  CEMENT  AND  CONCRETE 

powder  by  measuring  the  amount  of  liquid  which  it  will  dis- 
place. A  simple  form  of  apparatus  may  be  constructed  in 
any  laboratory  as  follows:  In  a  wide  mouth  bottle,  having 
straight  sides  and  holding  200  c.c.  or  more,  fit  a  perforated 
cork.  Through  the  cork  slip  a  burette  graduated  in  cubic 
centimeters  from  0  to  50,  placing  the  zero  end  down.  Fill  the 
bottle  and  the  tube  up  to  the  zero  mark,  with  some  liquid  such 
.as  turpentine,  benzine  or  kerosene  oil,  but  preferably  benzine 
(62°  Baume  naptha).  By  means  of  a  funnel  in  the  top  of  the 
burette,  add  slowly  100  grams  of  cement;  then  jar  the  bottle  to 
remove  air  bubbles  and  read  the  burette.  This  reading,  x, 
represents  the  volume  of  100  grams  of  cement;  and  100,  the 
volume  of  100  grams  of  water,  divided  by  x  gives  the  specific 
gravity  of  the  sample. 

63.  Among  other  forms  of  apparatus  which  are  also  of  sim- 
ple construction  and  tend  to  facilitate  the  test,  may  be  men- 
tioned the  following:  — 

M.  Candlot l  devised  an  apparatus  consisting  of  a  graduated 
tube  terminating  in  a  bulb  at  the  upper  end,  the  lower  end  of 
the  tube  being  ground  to  fit  the  neck  of  a  flask.  The  tube  and 
flask  being  disconnected,  sufficient  liquid  is  placed  in  the  bulb 
so  that  when  connected  with  the  flask  and  placed  upright,  the 
level  of  the  liquid  will  be  at  or  near  the  zero  mark  on  the  tube. 
The  actual  level  of  the  liquid  is  read  after  standing  a  few  minutes ; 
the  apparatus  is  again  inverted  and  the  flask  disconnected  to 
allow  of  the  introduction  of  100  grams  of  cement.  The  flask  is 
then  replaced  and  the  contents  of  the  apparatus  well  shaken  to 
expel  air-bubbles.  When  the  latter  have  been  completely  ex- 
pelled, the  flask  is  placed  upright,  and  after  standing  a  short 
time  the  level  of  the  liquid  is  again  read,  the  difference  between 
the  two  readings  indicating  the  absolute  volume  of  100  grams 
of  the  cement  powder. 

The  apparatus  devised  by  M.  H.  LeChatelier2  consists  of  a 
flask  of  a  capacity  of  about  120  c.c.,  and  having  a  neck  some 
20  c.  in  length,  halfway  up  which  is  a  bulb  having  a  capacity 


1  "Ciments  et  Chaux  Hydrauliques,"  par.  E.  Candlot. 

2  "Report  of  Commission  des  Methods  d'Essai  des  Materiaux    de  Con- 
struction," The  Engineer  (London);  Illustrated    also  in   Meade's   "Examina- 
tion of  Portland  Cement,"  Spaulding's  "Hydraulic  Cement,"  and  Engineer- 
ing News,  January  29,  1903. 


SPECIFIC  GRAVITY 


41 


-ip- 


-31- 


—30- 


c/ta  3mm 


of  20  c.c.  Near  the  bottom  of  the  tube,  or  flask,  is  the  zero 
mark,  and  above  the  bulb  the  tube  is  graduated  for  a  length 
corresponding  to  a  capacity  of  3  c.c.,  each  graduation  repre- 
senting .1  c.c.  The  diameter  of  the  tube  is  about  9  mm.  The 
zero  mark  on  the  tube  is  below  the  bulb.  The  method  of  opera- 
tion is  similar  to  that  described 
above. 

64.  The   following   style   of 
apparatus  (see  Fig.   1)    is  sug- 
gested   as    a    very    convenient 
form,  and  one  which   may  be 
used  for  another   test   soon   to 
be  described.     In  this  form,  the 
flask,   of  a    capacity  of   about 
200  c.c.,  has  straight  sides  and 
a  flat  bottom.     The  lower  part 
of  the  burette  is  of  large  diame- 
ter, about  15  mm.,  to  allow  the 
cement    to   pass  readily,  while 
the     upper     portion    is    made 
smaller,  about  8  mm.,  to  per- 
mit more  accurate  reading,  and 
is  graduated  from  30  c.c.  to  40 
c.c.,  the  divisions  being  0.1  c.c. 
Half    divisions    may    be    esti- 
mated.   The  zero  mark  is  in  the 
larger  part  of  the  burette,  but  it 
is  less  difficult  to  make  an  ac- 
curate reading  at  the  zero  mark, 
since  at  the  time  of  taking  this 
reading  the  liquid  is  clear;  this 
mark  should  entirely  surround 
the  burette.    The  mouth  of  the 
bottle  and  the  lower  end  of  the 
burette  should  be  ground  to  fit, 

and  a  ground  glass  stopper  should  form  a  part  of  the  apparatus. 
A  long  pipette  will  be  found  convenient  for  adjusting  the  level 
of  the  liquid  to  the  zero  mark. 

65.  Turpentine  is  frequently  employed  for  this   test,  but  it 
is   somewhat  inconvenient   to  use,  since  its  volume  is  so  sensi- 


o  — \//*r/t/e  eft*.  IS  mm. 

/        \ 


FIG.  1.  — SPECIFIC  GRAVITY  APPA- 
RATUS 


42  CEMENT  AND  CONCRETE 

live  to  changes  in  temperature.  This  sensitiveness  renders  it 
imperative  that  the  temperature  at  the  time  of  taking  the  final 
reading  be  the  same  as  when  the  initial  reading  is  taken,  or 
that  a  correction  be  applied.  To  assure  this  condition  the  ap- 
paratus should  be  immersed  in  a  water  bath,  and  the  tempera- 
ture of  the  cement  should  be  the  same  as  that  of  the  turpentine. 
The  use  of  water  in  the  apparatus  does  not  offer  this  inconven- 
ience, but  it  is  possible  that  the  hydration  of  the  cement  during 
the  experiment  might  be  sufficient  to  so  affect  the  volume  as 
to  change  the  result,  especially  with  quick-setting  cements. 
Light  oils,  such  as  benzine  and  kerosene,  are  rather  volatile, 
but  the  former  (62°  Baume  naptha)  is  recommended  in  the 
preliminary  report  of  the  Committee  of  the  American  Society 
of  Civil  Engineers.  With  the  precautions  mentioned  above, 
turpentine  may  be  used  with  good  results;  that  which  has 
been  dried  by  standing  over  cement  or  quicklime  is  to  be 
preferred. 

66.  This  test  may  be  extended  to  give  interesting  and  valu- 
able results,   in  the  following  manner:  When  the  cement  has 
settled  in  the  bottle,  leaving  the  liquid  clear,  pour  off  a  portion 
of  the  latter  and  replace  the  burette  by  a  glass  stopper.     Thor- 
oughly agitate  the  remaining  liquid  and  cement  until  the  latter 
is  in  suspension;  allow  the  cement  to  settle  again  without  dis- 
turbance, and  it  will  be  found  that  it  is  graded  in  the  bottle 
according  to  its   fineness,   the   coarsest  particles  being  at  the 
bottom.     With  Portland  cement,  if  a  portion  of  the  sample  is 
underburned  it  will  appear  as  the  top  layer,  and  be  indicated 
by  its  yellow  color.     It  will  also  be  interesting  to  note  what 
proportion  of  the   cement  is  so  fine  that  the  separate  grains 
are   indistinguishable.     That   the   bottle   should   have   straight 
sides  and  a  flat  bottom  is  to  accommodate  this  part  of   the 
test,    which  also  dictates   the  use  of   some  other   liquid    than 
water. 

67.  Effect  of  Composition,  Aeration,  Etc.  —  It  has  been  said 
above   that   the   composition   of   a   cement   affects   its   specific 
gravity,  a  highly  limed  cement  having  a  higher  density.     On 
this  account  an  analysis  for  lime  is  valuable  in  connection  with 
this  test,  in  order  to  determine  whether  a  high  specific  gravity 
is  due  to  a  high  percentage  of  lime  or  to  hard  burning. 

The  age,  or  aeration  of  a  sample  affects  its  specific  gravity 


SPECIFIC  GRAVITY  43 

because  of  the  absorption  of  water  from  the  atmosphere.  The 
absorption  of  two  per  cent,  of  water  is  sufficient  to  lower  the 
specific  gravity  from  3.125  to  3.000.  The  following  may  be 
given  as  illustrating  this  point:  a  certain  sample  of  natural 
cement  when  taken  from  the  barrel  had  a  specific  gravity  of 
3.106;  after  it  had  been  spread  out  in  the  air  for  two  months  its 
specific  gravity  was  3.000.  A  quantity  of  this  aerated  cement 
weighing  120  grams  was  placed  in  an  iron  vessel  and  heated 
over  an  oil  stove  for  about  one  hour;  at  the  end  of  this  time 
the  cement  had  lost  two  grains  in  weight.  The  specific  gravity 
of  the  fresh  cement  being  3.106,  118  grams  would  have  an  ab- 
solute volume  of  33  c.c.;  two  grams  of  water  would  occupy  2 
c.c.,  hence  120  grams  of  the  aerated  cement  would  occupy  40 
c.c.,  and  120  -r-  40  =  3.00,  the  specific  gravity  of  the  aerated 
cement  as  found  above.  It  is  not  always  possible  to  thus 
drive  off  all  of  the  water  absorbed,  since  a  portion  of  it  may 
enter  into  combination  with  the  cement;  but  a  sample  should 
always  be  heated  for  at  least  thirty  minutes  at  a  temperature 
of  100°  C.  before  making  the  test  for  specific  gravity,  and 
should  any  appreciable  loss  of  weight  occur,  it  is  an  indication 
of  aeration. 

68.  A  determination  of  the  specific  gravity  is  primarily  a 
test  for  burning,  but  it  may  also  be  of  much  value  in  detecting 
adulterations,  as  with  blast  furnace  slag  or  ground  limestone. 
An  admixture  of  10  per  cent,  of  either  of  these  substances  would 
suffice  to  lower  the  specific  gravity  from  3.15  to  about  3.10. 
The  specific  gravity  of  Portland  cement  ranges  from  2.90  to 
3.25,  but  a  first-class  product  should  not  show  a  lower  specific 
gravity  than  3.05.  If  fresh  Portland  gives  a  result  below  this 
it  is  probably  either  underburned  or  underlimed,  or,  perhaps, 
has  been  adulterated. 

The  specific  gravity  of  natural  cements  has  been  found  to 
vary  from  2.82  to  3.25.  The  specific  gravity  of  one  sample  of 
underburned  natural  cement  was  found  to  be  lower  than  a 
sample  of  the  same  brand  which  was  overburned,  but  it  seems 
very  doubtful  whether  this  is  true  of  other  brands  made  from 
rock  of  a  different  character.  It  was  also  found  that  the  spe- 
cific gravity  of  the  coarse  particles  of  some  natural  cements  is 
lower  than  that  of  the  fine  particles  (see  Table  10,  Art.  15), 
while  the  opposite  is  true  in  the  case  of  Portland  cements. 


44  CEMENT  AND  CONCRETE 

No  general  rules  can  be  given  at  present  for  the  interpreta- 
tion of  this  test  that  are  applicable  to  all  natural  cements;  it  is 
thought  that  the  test  will  be  of  value  in  comparing  samples 
of  the  same  brand,  though  it  seems  doubtful  whether  it  will 
prove  of  value  in  comparing  one  brand  of  natural  cement  with 
another,  since  it  is  quite  probable  that  the  interpretation  may 
vary  with  the  variety  of  rock  used  in  the  manufacture.  The 
value  of  the  test  for  Portland  cements  is,  however,  well 
established. 


CHAPTER  VI 

SIFTING   AND    FINE   GRINDING 

ART.  14.    FINENESS 

69.  Importance  of  Fineness.  —  The  fineness  of  cement  is  al- 
ways conceded  to  be  one  of  its  most  important  qualities,  and 
the  determination  of  fineness  is  omitted  in  none  but  the  very 
crudest  tests.     Unfortunately,  however,  sieves  that  are  so  coarse 
as  to  give  delusive  results  are  usually  employed.     It  is  very  easy 
to  show  that  grains  of  cement  as  large  as  one-fiftieth  of  an  inch 
in  diameter  are  practically  valueless,  but  much  more  difficult 
to  determine  the  point  of  fineness  at  which   the  particles  begin 
to  have  cementitious  value. 

70.  A  moderately  coarse  sieve  is  easier  to  operate  than  a 
very  fine  one,  less  time  being  consumed  in  sifting.     The  impres- 
sion seems  to  be  quite  general  also  that  there  is  a  fixed  relation 
between  the  proportions  of  the  different  sized  grains  in  different 
samples.     Many  specifications  require  that  a  certain  percentage 
"  shall  pass  a  sieve,  having  2,500  holes  per  square  inch."     Now, 
there  is  little  doubt  that  grains  of  cement  larger  than  .005  inch 
in  one  dimension  have  very  little  cementitious  value,  and  hence 
a  cement,  all  of  which  would  pass  holes  .015  inch  square,  while 
but  50  per  cent,  of  it  would  pass  holes  .005  inch  square,  is  little 
better  than  one  which  leaves  a  larger  residue  on  the  coarser 
sieve  but  the  same  residue  on  the  finer. 

In  America  and  Germany  it  is  the  usual  practice  in  the  pro- 
cess of  manufacture  to  pass  the  cement  through  a  screen  which 
will  reject  particles  larger  than  about  .015  inch  in  diameter;  the 
futility  in  attempting  to  determine,  with  a  sieve  no  finer  than 
this,  the  proportion  of  the  particles  which  are  fine  enough  to  be 
of  value,  is  therefore  apparent.  Since  the  English  cement 
makers  have  not  been  so  progressive  in  the  practice  of  screen- 
ing, they  have  obtained  the  reputation  of  producing  a  coarse 
product.  In  many  cases  this  reputation  is  probably  a  just  one, 
but  when  tested  with  a  very  fine  meshed  sieve,  some  of  the 

46 


46  CEMENT  AND  CONCRETE 

English  cements  do  not  compare  so  unfavorably  with  those  of 
German  manufacture.  It  is  a  curious  fact  in  this  connection 
that  the  English  are  the  most  conservative  in  holding  to  the 
use  of  the  coarse  sieve  in  testing,  which  makes  their  cement 
appear  so  very  much  coarser  than  the  American  or  German 
product. 

71.  SIEVES.  —  Sieves  for  cement  testing  may  be  made  either 
of  wire  or  silk  gauze,  set  in  metal  or  wood  frames.  Sieves  of 
perforated  metal  plate  are  sometimes  employed  for  sifting  sand, 
but  seldom  for  cement.  It  is  with  considerable  difficulty  that 
accurate  gauze  sieves  are  obtained.  They  are  usually  desig- 
nated by  numbers  corresponding  to  the  number  of  meshes  per 
linear  inch;  this  is  in  some  respects  an  unsatisfactory  method, 
for  the  size  of  the  wire,  which  is  quite  as  important  as  the 
number  of  meshes,  is  frequently  not  given  at  all,  or  stated 
in  terms  of  some  wire  gage  which  is  capable  of  various 
interpretations. 

As  usually  supplied  by  different  manufacturers,  sieves  pur- 
porting to  have  the  same  number  of  meshes  per  linear  inch  may 
vary  in  this  regard  as  much  as  10  or  15  per  cent.  Likewise  the 
size  of  wire  used  by  different  makers,  in  sieves  having  the  same 
number  of  meshes  per  inch,  may  vary  quite  as  much.  Again, 
on  account  of  irregularities  in  the  gauze,  the  holes  in  a  given 
sieve  vary  one  from  another;  in  some  cases  an  opening  may  be 
but  60  or  70  per  cent,  as  large  in  one  dimension  as  an  adjacent 
one. 

An  ideal  sieve  should  conform  to  the  following  requirements: 
(1)  holes  to  be  of  uniform  size  and  shape  throughout,  (2)  sides 
of  the  holes  to  be  very  smooth,  and  (3)  the  spaces  between  the 
holes  to  be  of  such  size  and  shape  that  particles  will  not  easily 
rest  there. 

It  is  evident  that  the  largest  holes  determine  the  character 
of  the  sieve.  For  example,  a  sieve  having  half  its  holes  0.01 
inch  square  and  the  other  half  0.02  inch  square,  would,  if  used 
long  enough,  separate  the  cement  exactly  as  it  would  if  all 
the  holes  had  been  0.02  inch  square.  Hence,  if  a  very  small 
percentage  of  the  holes  are  larger  than  the  normal,  it  seriously 
impairs  the  accuracy  of  the  sieve  by  introducing  an  indeter- 
mination;  but  holes  smaller  than  the  normal  have  no  greater 
objection  than  that,  as  the  sifting  proceeds,  they  become  spaces 


FINENESS 


47 


between  the  real  or  larger  holes,  and  as  such  do  not  fulfill  the 
third  requirement  mentioned  above.  The  shape  of  the  holes, 
whether  round,  square  or  hexagonal,  seems  of  minor  importance 
so  long  as  uniformity  is  maintained.  The  second  requirement 
is  necessary,  because,  should  particles  adhere  to  the  sides  of 
the  hole,  the  size  of  the  latter  would  be  decreased  to  that  ex- 
tent. The  third  requirement  is  for  convenience,  but  would 
require  consideration  if  the  style  of  the  sieve  were  changed  to  a 
punched  metal  plate. 

72.  The  Committee  of  the  American  Society  of  Civil  Engi- 
neers, in  their  report  on  "  A  Uniform  System  for  Tests  of  Cement " 
in  1885,  recommended  three  sizes  of  sieves  for  cement:  No.  50 
(2,500  meshes  to  the  square  inch)  wire  to  be  of  No.  35  Stubbs' 
wire  gage ;  No.  74  (5,476  meshes  to  the  square  inch)  wire  to 
be  of  No.  37  Stubbs'  wire  gage;  No.  100  (10,000  meshes  to  the 
square  inch)  wire  to  be  of  No.  40  Stubbs'  wire  gage.  For  sand, 
two  sieves  were  recommended,  No.  20  and  No.  30  (400  and  900 
meshes  per  square  inch)  wire  to  be  of  No.  28  and  No.  31  Stubbs' 

TABLE    5 

Sieves :  — Number  of  Meshes  per  Linear  Inch  and  Sizes  of 
Openings,  as  Found  by  Measurement 


No.  OP 

MESHES 

PKR 

DIAMETER  OF  WIRE 
IN  DECIMALS  OK 

MEAN  SIZE  OF  OPENING  IN  DECIMALS 
OF  AN  INCH. 

ff4 

o 

LINEAR 

AN  INCH. 

«  a 

INCH. 

b 

w  > 

M 

a  w 

^ 

(M 

. 

• 

— 

goo 

0> 
fcfc.     . 

8 

Web. 

Woof. 

8 

C  0> 

c! 

4J 

e 

O> 

•  « 

fc 

«! 

M 

a 
9 

Q}     M 

VI 

4)  •  — 

££ 

c 
v 

§•3 

1? 

§f- 
£ 

Diam- 

Diam- 

1 

55  ^ 

!•§ 

? 
11 

£ 

9 

tj 

S3 

IS  o 

Remarks. 

O 

*4 

e 

<J 

eter. 

eter. 

« 

.m£ 

W£ 

s 

af 

a 

b 

c 

(I 

e 

/ 

g 

h 

i 

j 

1 

20 

20 

19J 

.0185 

.0169 

.0016 

.0315 

.0337 

.0022 

.93 

2 

20 

20 

19 

.0105 

.0108 

.0003 

.0335 

.0358 

.0023 

.93 

3 

30 

30 

28  1 

.0119 

.0119 

.0000 

.0214 

.0229 

.0015 

.93 

4 

30 

30 

30 

.0118 

.0118 

.0000 

.0215 

.0215 

.0000 

1.00 

5 

30 

30 

29\ 

.0116 

.0122 

.0006 

.0217 

.0217 

.0000 

1.00 

6 

40 

40 

36 

.0395 

.0095 

.0000 

.0155 

.0183 

.0028 

.85 

7 

50 

60 

47 

.0082 

.0083 

.0001 

.0118 

.0130 

.0012 

.90 

8 

74 

80 

80 

.0054 

.0054 

.0000 

.0071 

.0071 

.0000 

1.00 

9 

100 

101 

88  1 

.0040 

.0040 

.0000 

.0059 

.0073 

.0014 

'   .80 

10 

120 

120 

120 

.0037 

.0037 

.0000 

.0046 

.0046 

.0000 

1.00 

It 

200 

210 

170 

.0022 

.0022 

.0000 

.0026 

.0037 

.0013 

.70 

Approx. 

CEMENT  AND  CONCRETE 


wire  gage,  respectively.  It  seems  to  be  impracticable  to  com- 
ply with  these  sizes  of  wires,  because  neither  manufacturers  nor 
engineers  appear  to  agree  as  to  what  diameters  of  wire  corre- 
spond to  No.  37  and  No.  40  Stubbs'  wire  gage. 

73.  The  conferences  of    Dresden  and  Munich  decided  that 
fineness  should  be  determined  by  sieves  of  900  and  4,900  meshes 
per  sq.   cm.,   respectively,   for  Portland   cement,   and   900  and 
2,500,  respectively,  for  other  hydraulic  products,  the  size  of  the 
wires  being  as  follows:  for  4,900,  .05  mm.;  for  2,500,  .07  mm.; 
and  for  900,   .10  mm.     These  sieves  would  have  respectively 
31,600  (178  X  178),   16,000  (127  X  127),  and  5,800  (76  X  76) 
meshes  per  square  inch,  and  the  sizes  of  the  holes  would  be 
approximately  .0037  inch  square,  .005  inch  square  and  .009  inch 
square,  respectively.     It  was  also  decided  that  for  sifting  sand, 
punched  metal  plates  were  preferable  to  wire  cloth  sieves. 

74.  In  Table  5  are  given  some  of  the  results  obtained  by  the 
writer  which  will  serve  to  show  what  variations  may  exist  in 
sieves  which  have  been   selected   from  a  considerable  number 
offered  for  use. 

Table  6  gives  the  data  available  concerning  certain  sieves 
that  have  been  used  or  recommended  in  this  country  and  else- 
where. 

TABLE   6 

Sizes  of  Openings  in  Sieves  Recommended  or  in  Use 


||  ' 

|g 

SIZE 

REF. 

||| 

£| 

HOLE, 
INCH 

REMARKS. 

ll 

Is 

SQUARE. 

a 

b 

c 

1 

178 

.00197 

.00366 

Established  by  Conferences,  Dresden  &  Munich. 

2 

127 

.00276 

.00512 

11                     U                        (I                                   U                                  it 

3 

76 

.00394 

.00920 

U                      U                       U                                   U                                 it 

4 

76 

.00437 

.00875 

Present  German  Standard. 

5 

76 

.00591 

.00721 

Recommended  by  H.  LeChatelier. 

6 

176 

.00162 

.004 

Silk  mesh  —  Vyrnwy  Reservoir. 

7 

103 

.0022 

.0075 

u           u               ct                    u 

8 

170 

.00279 

.00309 

Cornell  University,  Marx  &  Mosscrop,  1887. 

9 

80 

.00651 

.00599 

u                   u                   u                      u                  u 

10 

50 

.00881 

.01119 

H                             11                             it                                 U                           U 

11 

30 

.01214 

.02119 

u                   u                   u                      u                 u 

12 

20 

.01899 

.03101 

t(                           U                           <(                               U                        it 

13 

200 

.0024 

.0026 

Progress  Report,  A.  S.  C.  E.  Committee,  1903. 

14 

100 

.0045 

.0055 

11                         U                      U                    U                               U                           U 

SIFTING  AND  GRINDING 


49 


75.  The  time  sifting  should  be  continued  will  depend  on  the 
fineness  of  the  meshes,  the  diameter  of  the  sieve,  the  amount 
of  cement  taken,  and  the  manner  of  sifting  ;  it  will  also  depend 
upon  the  fineness  of  the  cement,  as  well  as  its  nature,  and  its 
condition  as  to  dryness.     But,  although  some  care  is  necessary 
concerning  these  points,  very  large  variations  in  results  due  to 
variations  in  the  time  the  sifting  is  continued  may  easily  be 
avoided.     The  diameter  of  the  sieve  is  usually  made  greater 
for  the  finer  meshes,  but  this  is  not  always  the  case.     It  is  a 
common  practice  in  America  to  use  one-tenth  of  a  pound  of 
cement  in  testing  the  fineness,  using  a  scale  weighing  in  ten- 
thousandths  of  a  pound.     Where   the   metric  system  is  in  use 
(and  it  may  well  be  adopted  in  a  cement  laboratory),  100  grams 
of  cement  are  usually  taken. 

76.  M.  H.  LeChatelier  recommends  a  sieve  having  900  meshes 
per  sq.  cm.,  of  wire  0.15  mm,  diameter,  giving  holes  0.18  mm. 
(.0072  inch)  square.     He  prefers  machine  screening,  but  says 
that  for  current  tests  it  might  be  sufficient  to  screen  by  hand 
for  ten  minutes  with  a  sieve  three  decimeters  (about  12  inches) 
in  diameter. 

Table  7  is  taken  from  experiments  made  by  M.  Durand- 
Claye  and  M.  Candlot,  and  shows  what  differences  may  arise 
from  varying  the  length  of  time  that  a  sample  is  screened.  The 
cements  used  were  not  the  same  in  the  two  cases,  but  the  sieves 
had  each  5,000  meshes  per  sq.  cm.  (about  180  per  linear  inch), 
and  100  grams  of  cement  were  taken  in  each  case.  Had  a  coarse 
sieve  been  used,  the  differences  would  have  been  much  less 
after  the  same  lengths  of  time. 

TABLE   7 

Fineness:  —  Mechanical  and  Hand  Sifting  Compared 


M.  DURAND-CLAYE. 

M.  CANDLOT. 

MECHANICAL  SIEVE  MAKING  200 

HAND  SIEVE,  12  INCHES  IN 

REVOLUTIONS  PER  MINUTE. 

DIAMETER. 

No. 
Revolutions. 

Per  Cent. 
Retained. 

Ditf. 

After 
Minutes. 

Per  Cent. 
Retained. 

Diflf. 

500 

41.2 

5 

29.6 

1,000 

39.4 

1.8 

10 

29.1 

0.5 

1,500 

38.6 

.8 

20 

28.4 

0.7 

2,000 

38.0 

.6 

30 

28.0 

0.4 

2,500 

37.6 

.4 

40 

27.7 

0.3 

50 


CEMENT  AND  CONCRETE 


77.  Table  8  gives  the  results  obtained  by  the  author  in 
sifting  several  samples.  The  No.  80  sieve  was  about  6J  inches 
in  diameter,  and  Nos.  120  and  200  about  5J  inches.  One  hun- 
dred grams  of  cement  were  taken  in  each  case,  and  the  sieve 
was  shaken  vigorously  by  hand.  It  is  seen  that  coarse  samples 
require  less  time  for  sifting  than  fine  samples,  arid  that  natural 
cements  require  a  longer  time  than  Portlands.  With  the  No. 
80  sieve,  five  minutes  usually  suffices  to  obtain  the  fineness, 

TABLE   8 

Effect  of  Time  of  Sifting  on  the  Result  Obtained  in  Testing 

Fineness 


« 

I 

» 

1 

2 
3 
4 

5 
6 

7 
8 

9 

10 
11 
12 
13 
14 
15 
16 

17 

18 
19 
20 
21 
22 
23 
24 

SIEVE. 

CEMENT. 

PEK  CENT.  BY  WEIGHT  THAT  HAD 
PASSED  SIEVE  AFTER  SIFTING. 

*§ 

2-S.a 
c  o>  « 

| 

ad  a 
^fc 

-  ^5 

II 
M 

^M 

Kind. 

Brand. 

Sam- 
ple. 

1 
% 

o> 
3 

a 

i 

eo 

1 

3 

a 

i 

1O 

I 
a 

a 

§ 
t- 

1 

§ 

O 

1 
1 
S 

k 

1 

c 

i 
s 

i 

I 

3 

1 
8 

a 

b 

c 

d 

e 

f 

<7 

h 

93 

86 
96 

i 

j 

m 

80  j 

u 

u 

u 

120  j 

it 
It 
u 
1  1 
(( 
(( 
it 

200  j 

u 

t< 
t( 

(  t 

.0071 

by 

.0071 

(4 

U 

(i 
(( 

.0046 

by 

.0046 
t 

i 
( 

i 
t 

.0036 
by 
.0037 

i 

( 

( 

i 

Port. 

u 

u 

Nat. 

u 

ii 
u 

Port. 

u 
(i 

u 

Nat. 
u 
« 

Port. 

1  1 

u 
('( 

Nat. 

n 

u 
it 

X 

Y 

S 
Z 

Bti 

An 
In 
Gn 

X 

Y 

8 
Z 
Bn 
An 

In 
Gn 

X 

Y 

S 
Z 

Bn 

An 
In 
Gn 

685 

42s 
34s 
43s 
27s 
G 
28s 
108  T 

685 

42s 
34s 
43s 

27s 
G 
28s 
108  T 

685 

42s 
34s 
43s 
27s 
G 
28s 
108  T 

91 

82 
95 
100 
68 
78 
85 
75 

45 

41 

72 
54 
27 
45 
13 
5 

92 

85 

96 

93 

71 

80 
89 
89 

78 

73 
89 
94 
62 
73 
42 
16 

58 

65 
72 
74 
57 
67 
41 
40 

71 
82 
90 
90 

82 

77 
90 
96 
65 
76 
64 
27 

65 

68 
76 
78 
59 
69 
53 
49 

82 
90 
91 

v  • 

91 
84 

78 
91 
97 
66 
78 
82 
64 

68 

71 
78 
81 
60 
70 
69 
64 

84 

78 
91 
98 
66 
78 
83 
82 

70 

72 

80 
82 
60 
72 
75 
76 

So 
71 

72 
81 
83 

*72 

77 
79 

86 
7*8' 

FINENESS 


and  with  the  No.  120  sieve,  but  little  cement  usually  passed  after 
the  sifting  had  continued  ten  minutes,  though  with  one  brand 
of  natural,  Gn;  it  appears  that  the  true  fineness  would  not  be  in- 
dicated by  sifting  less  than  20  minutes.  With  the  No.  200 
sieve  20  minutes  is  usually  required,  and  in  the  case  of  two  samples 
of  natural  cement,  a  still  longer  time  appears  to  be  necessary. 

78.  Conclusions.  —  Until   there  is  a  proper  standard  in  the 
United  States  concerning  sieves  and  methods  of  sifting,  the  best 
that  can  be  done  is  to  select,  from  the  sieves  that  manufacturers 
have  to  offer,  those  which  appear  to  be  most  nearly  uniform  in 
size  of  mesh,  and  then  actually  determine  the  size  of  the  holes. 
This  may  be  done  by  counting,  under  the  magnifying  glass,  the 
number  of  meshes  per  inch  each  way,  and  determining  the  size 
of  wire  with  a  micrometer  wire  gage. 

As  to  the  time  sifting  should  be  continued,  one  can  easily 
find  by  trial  the  time  required  in  using  a  given  sieve  in  order  to 
confine  the  error  within  given  limits.  A  fine  natural  cement 
should  be  selected  to  determine  this,  as  such  a  cement  requires 
the  longest  sifting.  Care  should  be  taken  that  the  cement  is 
well  dried  before  making  the  test  for  fineness.  It  will  be  found 
that  for  sieves  having  holes  between  .003  inch  and  .004  inch 
square  (sieves  approximating  170  to  200  meshes  per  linear 
inch)  20  to  30  minutes  are  required,  while  for  sieves  having 
holes  .007  to  .009  inch  square  (approximately  70  to  100  meshes 
per  linear  inch)  from  five  to  ten  minutes  will  usually  suffice. 

79,  Specifications  for  Fineness.  —  The  following  table   has 
been  compiled  to  show  what  are  considered  reasonable  require- 
ments for  fineness.     In  most  specifications  there  is  the  usual 
indeterminatkm  concerning  the  sizes  of  holes  in  the  sieves. 

TABLE   9 
Requirements  as  to  Fineness 


SPECIFICATION. 

DATE. 

PERCENT.  REQUIRED  TO  PASH 
SIEVE  HAVING  10,000 
HOLES  PER  SQUARE  INCH. 

Portland. 

Natural. 

U.  S.  Army  Engineers  .... 
U.  S.  Navy  Department  .  .  . 
City  Pittsburg  Pa.  .  .  . 

1901 

1900 
1897 
1896 
1895 

92 
95 
90 
90 
95 
85 

80 

'•11 

'80* 

New  East  River  Bridge  .  .  . 
Topeka,  Kan.,  Bridge  .  .  . 
Master  Builders'  Exchange,  Phila. 

CEMENT  AND  CONCRETE 


ART.  15.  COARSE  PARTICLES  IN  CEMENT 
80.  The  Effect  of  Coarse  Particles  on  the  Weight  of  Cement. 
—  To  remove  the  coarse  particles  by  sifting  will  reduce  the 
specific  gravity  of  a  sample  of  Portland  cement,  as  the  un- 
ground  particles,  are  from  the  harder  burned  and  denser  por- 
tion of  the  clinker,  and  to  remove  these  denser  particles  will, 
of  course,  decrease  the  average  density  of  the  sample.  This  is 
not  always  the  case  with  natural  cements,  as  is  shown  by  the 
following  tests:  — 

TABLE   10 

The  Relative  Specific  Gravity  of  Coarse  and  Fine  Particles  of 

Cement 


CEMENT. 

Kind. 

Brand. 

Fineness. 

SPECIFIC  GRAVITY. 

Portland 

R 

As  received    . 

3.086 

if 

50-100 

3  14") 

X 

Pass  50      . 

8.039 

»« 

Ret.  on  50 

3.125 

Nati  ral 

Gu 

Pass  100    . 

2.874 

u 

Ret  on  50 

2.817 

An 

Pass  50      . 

2.945 

" 

Ret.  on  50 

2.817 

The  apparent  density  or  weight  per  cubic  foot  of  Portland 
will  be  reduced  more  than  the  specific  gravity  by  the  removal 
of  the  coarse  particles;  because  not  only  will  the  true  density 
be  decreased,  but  the  packing,  which  is  facilitated  by  a  wide 
range  in  the  sizes  of  the  particles,  will  be  less  perfect  than  when 
the  coarse  particles  are  present.  In  §  89  a  table  is  given  show- 
ing the  changes  in  specific  gravity  and  weight  per  bushel  oc- 
casioned by  removing  the  coarse  particles  by  sifting. 

81.  Effect  of  Coarse  Particles  on  the  Time  of  Setting.  — 
Table  11  gives  the  results  of  a  number  of  tests  on  Portland  and 
natural  cements  to  determine  the  relative  time  of  setting  of 
samples  from  which  the  coarse  particles  had  been  removed  by 
the  No.  200  sieve,  while  Table  12  gives  results  obtained  with 
a  sample  of  natural  cement  of  varying  fineness. 

In  Table  11,  30  per  cent,  of  water  was  used  for  all  Portland 
cements,  and  36  per  cent,  for  all  naturals,  but  the  consistency 


COARSE  PARTICLES 


varied  as  stated  in  the  table.  It  is  seen  that  in  nearly  every 
case  the  setting  was  hastened  by  removing  the  coarse  particles, 
though  this  may  have  been  due  in  part  to  the  fact  that  with  the 
same  percentage  of  water  the  finer  cement  gave  a  stiffer  paste. 
For  the  tests  in  Table  12,  the  attempt  was  made  to  make  all 
of  the  mortars  of  the  same  consistency  by*varying  the  percent- 
age of  water.  As  would  be  expected,  the  coarse  particles  are  very 
slow  setting.  In  fact,  what  hardness  they  attained  was  prob- 
ably due  largely  to  the  fine  dust  that  adhered  to  the  grains. 
These  coarse  particles  may  be  considered  as  practically  inert, 
and  their  presence  in  a  sample  would  naturally  make  it  slow 
setting.  To  show  this  by  actual  test,  however,  is  very  difficult, 

TABLE   11 

Effect  of  Coarse  Particles  011  the  Time  of  Setting 


CEMENT. 

CKMKNT  PASSING  No.  20 
SIEVE. 

CKMKNT  PASSING  No.  liOO 
SIEVE. 

Time  to  bear 

Time  to  bear 

Kind. 

Brand. 

i   Ib.   wire. 

Consistency. 

i    Ib.    wire. 

Consistency. 

Minutes. 

.Minutes. 

Portland 

Y 

39 

Trifle  moist 

13 

Trifle  dry 

it 

X 

9 

Moist 

4 

0.  K. 

ii 

Z 

432 

Trifle  moist 

354 

Trifle  dry 

it 

S 

550 

(I                  U 

341 

U             li 

Natural 

Gn 

31 

29 

H 

Bn 

143 

Trifle  moist 

161 

Trifle  dry 

U 

In 

397 

41                   t  I 

250 

. 

II 

Un 

256 

.          .          . 

233 

•     •     • 

NOTE:  —  30  per  cent,  water  used  for  all  Portlands. 

36  per  cent,  water  used  for  all  natural  cements. 

TABLE   12 
Effect  of  Coarse  Particles  on  Time  of  Setting 

Natural  Cement,  Brand  Gn  —  All  pastes  appeared  same  consistency, 


WATER  USED  AS 

TIME  TO  BEAR 

TIME  TO  BEAR 

FINENESS. 

PER  CENT.  OF 

i  LB.  WIRE. 

1  LB.  WIRE. 

CEMENT. 

Minutes. 

Minutes. 

Pass  No.    20  sieve 

33 

14 

159 

"          50    " 

36 

29 

219 

"        100    " 

38 

24 

214 

Retained  on  50," 

reground  to  pass  100 

28 

73 

070 

Pass   No.    50.    retained 

on  No.  100 

34 

205 

890 

54  CEMENT  AND  CONCRETE 

as  the  amount  of  water  required  to  bring  the  mortars  to  the 
same  consistency  varies  with  the  amount  of  coarse  particles 
present,  and  as  there  is  no  very  satisfactory  method  of  testing 
the  consistency,  the  tests  for  time  of  setting  have  in  them  this 
indetermination. 

82.  Effect  of  Coarse  Particles  on  the  Tensile  Strength.  —  A 
cement   having  a  certain  quantity  of  coarse  particles  will  fre- 
quently give  a  higher  tensile  strength  when  tested  neat  than  a 
cement  from  which  the  coarse  particles  have  been  removed  by 
screening.     The  reason  for  this  may  be  found  in  the  fact  that 
a  wide  range  in  the  sizes  of  grain  of  the  powder  facilitates  pack- 
ing, both  when  dry  and  when  mixed  with  water  to  form  a  paste. 
Another   reason    is   that  the  unground    particles    are    stronger 
than  the  hardened  mortar,  and,  considering  the  broken  section 
of  a  briquet,  the  break  does  not  take  place  through  these  par- 
ticles, but  they  are  pulled  out  of  their  bed;  this  virtually  in- 
creases the  area  of  section.     Were  the  same  sample  of  cement 
reground,  so  that  a  certain  proportion  of   the  coarse  particles 
was  rendered  active,  it  might  then  give  a  higher  strength,  neat, 
than  at  first.     If  so,  the  reason  would  be  found  in  the  fact  that 
the  coarse  particles,  being  the  hardest  burned,  were  really  from 
the  best  part  of  the  cement  clinker,  and  rendering  these  parti- 
cles active  by  fine  grinding  increased  the  cohesive  properties  of 
the  cement  so  much  as  to  overcome  the  physical  effect  of  the 
coarse  particles,  which,  when  judged  by  neat  tests,  appear  to  be 
beneficial.      The  above  serves  to  illustrate  the  difference  be- 
tween  sifting  and  fine  grinding  which  are  so  frequently  con- 
fused in  treating  this  subject. 

83.  Among  the  many  tests  that  have  been  made  to   show 
the  effect  of  sifting  on  the  cohesive  and  adhesive  strength  of 
cements,  a  few  may  be  given  as  follows:  — 

Mr.  Maclay l  gives  a  few  experiments  to  show  that  the  pres- 
ence of  coarse  particles  increases  the  cohesive  strength,  neat, 
seven  days. 

Lieut.  W.  Innes2  gives  two  tables  of  results  obtained  by  ex- 
perimenting on  very  coarse  cements.  The  tables  show  that 
removing  the  particles  that  would  not  pass  through  sieves  of 


1  Trans.  Am.  Soc.  C.  E.,  Vol.  vi. 

2  Minutes  Proc.  Inst.  C.  E.,  Vol.  xxv. 


COARSE  PARTICLES  55 

1,296  meshes  and  2,500  meshes  per  square  inch,  decreased  the 
strength  when  tested  neat  at  the  ages  of  three  months  and  six 
months;  but  increased  the  strength  when  sand  mortars  were 
used.  The  differences  at  six  months  were  relatively  somewhat 
less  than  at  three  months.  By  separating  a  sample  of  cement 
into  two  parts,  that  passing  a  sieve  having  2,500  meshes  per 
square  inch  and  that  retained  on  the  same  sieve,  and  then 
remixing  the  screenings  with  the  fine  portion,  he  found 
that  the  highest  strength,  neat,  six  months,  was  given  by  the 
mixture  containing  the  largest  amount  tried  (70  per  cent.)  of 
screenings. 

84.  Jn  the  tests  of  cement  for  the  Cairo  Bridge1  a  series  of 
experiments  was  made  to  determine  the  effect  of  coarse  parti- 
cles on  the  value  of  both  Portland  and  natural  cements.     The 
cement  was  separated  into  two  parts,  by  a  sieve  having  10,000 
meshes  per  square  inch.     Briquets  were  made  both  neat  and 
with  sand,  the  cement  used  being  made  of  100,  90,  80,  70  and 
60  volumes  of  sifted  cement  to  0,  10,  20,  30,  and  40  volumes, 
respectively,  of  cement  screenings.     The  briquets  were  broken 
when  six  months  old. 

It  was  found  that  in  the  case  of  Portland  cement,  neat,  the 
highest  result  was  obtained  with  the  largest  (40)  per  cent,  of 
screenings,  but  with  one  and  two  parts  sand,  the  strength 
steadily  fell  as  larger  amounts  of  screenings  were  used.  With 
Louisville  natural  cement  the  presence  of  screenings  seemed  to 
have  little  effect  on  neat  tests;  and  with  one  part  of  sand  to  one 
of  cement,  the  use  of  as  much  as  30  per  cent,  of  screenings  to 
70  per  cent,  of  sifted  cement  did  not  appear  to  decrease  the 
strength.  With  two  parts  sand  to  one  cement,  the  results  were 
slowly  diminished  by  successive  additions  of  larger  percentages 
of  screenings. 

85.  M.  R.  Feret  is  said  to  have  replaced  with  sand  the  grains 
of  cement  retained  on  sieves  having  5,800  and  32,300  meshes 
per  square  inch,  and  found  that,  except  in  the  case  of  neat  ce- 
ment mortars,  the  substitution  of  sand  for  coarse  particles  of 
cement  did  not  decrease  the  strength.     In  experimenting  on 
this  subject  Mr.  Eliot  C.  Clarke 2  found  that  the  coarse  particles 


1  Jour.  Assn.  Engr.  Soc.,  1890,  and  Engineering  News,  Jan.  31,  1891. 

2  Trans.  A.  S.  C.  E.,  Vol.  xiv,  pp.  158-162. 


CEMENT  AND  CONCRETE 


TABLE  13 
Effect  of  Removing   Coarse   Particles  from    Natural  Cement 


CEMENT. 

No.  PARTS 
SAND  TO 
ONE 
CEMENT 

BY 

WEIGHT. 

WATER  AS 
PER 
CENT.  OF 
WEIGHT 
DRY 
INGREDI- 
ENTS. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

7  da. 

28  da. 

3  mo. 

6  mo. 

2  years. 

A 

None 

33.3 

120 

275 

B 

u 

35.7 

100 

206 

' 

C 

" 

38.5 

83 

253 

. 

D 

it 

28.3 

202 

264 

. 

. 

E 

n 

35.0 

127 

143 

.    .    . 

.    .    . 

.    .    . 

A 

One 

19.0 

121 

253 

330 

380 

B 

u 

19.6 

104 

251 

344 

398 

C 

tt 

20.0 

94 

261 

331 

385 

D 

(( 

16.0 

286 

360 

.    .    . 

396 

385 

A 

Two 

16.1 

168 

215 

223 

210 

B 

it 

16.1 

. 

203 

245 

267 

302 

C 

u 

16.1 

. 

218 

297 

317 

358 

D 

u 

13.9 

. 

227 

230 

245 

262 

E 

u 

15.8-16.1 

.  .  . 

71 

40 

57 

50 

A 

Three 

14.5 

127 

128 

B 

u 

14.5 

. 

167 

164 

C 

u 

14  5 

. 

. 

205 

234 

D 

l( 

12.1 

125 

118 

Fineness  of  Cement 


* 

PER  CENT.  PASSING  SIEVE  No. 

50 

100 

120 

Cement  A        .     .          .... 

82 
100 

70 
85 
100 

64 

78 
91 

Cement  B        

Cement  C        

NOTE  :  —  All  cement  from  same  barrel,  Brand  Bn,  Sample  27s. 

Sand,  crushed  quartz  20-30. 

All  briquets  made  by  one  molder  and  stored  in  one  tank. 

All  results,  mean  of  5  briquets,  except  two  which  are  means  of 

ten  and  two  briquets,  respectively. 

A  —  Cement  passing  No.    20  sieve,  holes  .033    inch  square. 
B—        "  "         "     50      "          "     .012  " 

C-  "         "    100      "          "     .0065 

D  —        "       retained  on  No.  50,  reground  to  pass  No.  100. 
E  —         "       passing  No.  50,  retained  on  No.  100. 


COARSE  PARTICLES 


57 


of  cement  were  somewhat  better,  for  use  in  mortar,  than  fine 
sand,  but  very  little  better  than  coarse  sand. 

86.  The  tests  given  in  Table  13  were  made  under  the  au- 
thor's direction  to  determine  the  effect  of  sifting  and  the  value 
of  coarse  particles.     It  is  seen  that  in  neat  tests  the  strength  is 
slightly  diminished  by  sifting  out  the  coarse  particles;  in  the 
tests  of  mortars  containing  equal  parts  by  weight  of  sand  and 
cement,  there  is  little  difference  in  the  strength  of  the  three 
samples,  though  the  coarser  cement  appears  to  gain  its  strength 
a  little  more  rapidly.     With  two  parts  sand  to  one  of  cement, 
the  greater  value  of  the  fine  particles  is  very  noticeable,  and 
with  one-to-three  mortars  the  difference  is  still  more    marked, 
the  sifted  cement  giving  80  per  cent,  greater  strength  than  the 
unsifted. 

87.  In  Table   14  these  results  are  arranged  in  a  different 
way.     If  we  assume  that  the  particles  that  will  not  pass  the 
No.   120  sieve  are  not  cement  at  all,  but  equivalent  to  sand, 

TABLE   14 

Effect  on  Tensile  Strength  of  Removing  Coarse  Particles  from 
Natural  Cement 


PARTS  SANI>  AND 

PER  CENT. 

PARTS  SAND 

COAKSE  PAR- 

STRENGTH 

CEMENT. 

PASSING  SIEVE 

TO 

TICLES  TO  ONE 

OF  MORTAR  AFTER 

No.  120. 

ONE  CEMENT. 

PART 

Two  YEARS. 

FINE  PARTICLES. 

A 

64 

3 

5.2 

128 

B 

78 

3 

4.1 

164 

A 

64 

2 

3.7 

210 

C 

91 

3 

3.4 

234 

B 

78 

2 

2.8 

302 

C 

91 

2 

2.3 

358 

A 

64 

1 

2.1 

380 

B 

78 

1 

1.6 

398 

C 

91 

1 

1.2 

385 

and  that  all  particles  passing  this  sieve  are  cement,  we  obtain 
a  new  set  of  proportions  of  sand  to  cement.  Thus  the  sample 
of  cement  passing  No.  20  sieve,  sample  A,  would  be  composed 
of  64  parts  cement  and  36  parts  sand,  and  the  1  to  3  mortar 
would  have  in  reality  the  proportion  64  cement  to  336  sand,  or 
1  to  5.2.  It  is  seen  that  the  tensile  strength  bears  a  closer 
relation  to  the  richness  of  the  mortar  when  considered  in  this 
way.  There  is,  of  course,  no  abrupt  division  in  size  such  that 


58 


CEMENT  AND  CONCRETE 


TABLE   15 
Value  of  Coarse  Particles  of  Cement,  Natural  and  Portland 


REFERENCE  NUMBER. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

Neat  Cement. 

1  Part  Standard 
Sand  to  1  Cement 

3  Parts  Standard 
Sand  to  1  Cement. 

3  Parts  Limestone 
Screenings, 
(S8)  to  1  Cement. 

3  mos. 

4  mos. 

l  yr. 

3  mos. 

lyr. 

3  mos. 

lyr. 

3  mos. 

lyr. 

d 

e 

/ 

9 

h 

i 

j 

k 

1 

1 

2 
3 
4 

5 
6 
7 
8 
9 
10 

330 

259 
295 
306 
309 

390 
336 
334 
370 
343 

108 
193 
203 
102 
92 
378 
423 
455 
357 
362 

139 
217 
224 
106 
96 
395 
403 
469 
399 
354 

160 
269 
251 
137 
139 
472 
538 
561 
425 
405 

234 
332 
319 
170 
155 
589 
677 
676 
5(58 
506 

'  •  • 

630 
550 
621 
615 
591 

706 
553 
665 
651 
764 

786 
755 
745 
746 
765 

812 
838 
891 
841 
837 

Ref.  No. 


Natural  cement  passing  No.  20  sieve. 
"  "  2.  Natural  cement  passing  No.  80  sieve. 
"  "  3.  Natural  cement  reground  before  sifting,  until  all  passed 

No.  80  sieve. 

"  "  4.  Natural  cement,  64f  per  cent,  of  cement  passing  No.  80 
sieve  mixed  with  35}  per  cent,  of  limestone  screen- 
ings retained  between  Nos.  20  and  80  sieves. 

"       "      5.   Natural  cement,  64f  per  cent,  of  cement  passing  No.  80 
sieve   mixed  with  35^  per  cent,  of  crushed   quartz 
retained  between  Nos.  20  and  80  sieves. 
"       "      6.    Portland  cement  passing  No.  40  sieve. 
"       "      7.    Portland  cement  passing  No.  80  sieve. 
"       "      8.    Portland  cement  reground  (before  sifting)  until  all  passed 

No.  80  sieve. 

"  "  9.  81§  per  cent,  of  cement  passing  No.  80  sieve  mixed  with 
18£  per  cent,  limestone  screenings  retained  between 
Nos.  40  and  80  sieves. 

"  "  10.  81§  per  cent,  of  cement  passing  No.  80  sieve  mixed  with 
18 J  per  cent,  crushed  quartz  retained  between  Nos. 
40  and  80  sieves. 

Of  the  natural  cement  passing  No.  20  sieve,  35|  per  cent,  was  retained 
on  sieve  No.  80,  while  64f  per  cent,  passed  the  No.  80  sieve.  In  lines  4  and 
5  the  coarse  particles  of  cement  (20-80)  were  removed  and  replaced  by  an 
equal  weight  of  sand  grains,  retained  between  sieves  20  and  80. 

Of  the  Portland  cement  passing  No.  40  sieve,  18£  per  cent,  was  retained 
on  sieve  No.  80,  while  81  §  per  cent,  passed  sieve  No.  80.  In  lines  9  and  10 
the  coarse  particles  of  cement  (40-80)  were  removed  and  replaced  by  an  equal 
weight  of  sand  grains  retained  between  sieves  40  and  80. 

All  briquets  made  by  same  molder,  each  result  mean  of  five  specimens, 


FINE  GRINDING  59 


coarser  particles  act  only  as  sand,  while  finer  ones  enter  into 
combination  as  cement;  part  of  the  coarse  particles  will  have 
some  cementitious  value,  while  some  of  the  finer  particles  will 
have  somewhat  the  effect  of  sand. 

As  to  the  sample  composed  of  coarse  particles  reground,  it 
must  be  considered  that  although  this  sample  was  passed  through 
the  No.  100  sieve,  yet  it  was  in  reality  much  coarser  than  sam- 
ple C,  because  the  particles  \vere  harder,  and  the  grinding 
in  the  mortar  less  thorough  than  the  original  grinding.  Since 
this  sample  of  reground  cement  gives  so  high  a  strength  neat 
and  with  one  part  sand,  it  appears  that  the  hard  particles  from 
which  it  was  made  are  of  excellent  quality  if  ground  fine  enough, 
and  the  relatively  lower  results  with  larger  proportions  of  sand 
must  be  attributed  to  imperfect  grinding. 

The  coarse  particles  retained  between  sieves  50  and  100  gave 
a  higher  strength  neat  than  was  expected,  but  much  of  this 
strength  may  be  due  to  the  floury  portion  of  the  cement  that 
doubtless  adhered  to  the  coarse  particles  instead  of  passing 
through  the  sieve. 

88,  The  tests  in  Table  15  were  made  to  determine  whether 
the  coarse  particles  of  cement  are  of  greater  value  in  mortar 
than  the  same  quantity  of  fine  sand.     The  coarse  particles  of 
the  cement  were  sifted  out  and  replaced  with  sand  grains  of 
about  the  same  size.     The  conclusion  drawn  from  the  preced- 
ing tests  would  indicate  that  some  of  the  coarse  particles  of 
cement   might   be   replaced   by   sand   without   diminishing   the 
tensile  strength;  but  the  tests  given  in  this  table  indicate  that 
this  is  not  the  case  when  it  is  a  question  of  substituting  sand 
grains   of   the   same   size.     Although   such   a   substitution   has 
little  effect  on  the  strength  of  rich  mortars,  it  results  in  a  de- 
creased  strength   with   mortars   containing   as   much   as   three 
parts  sand  to  one  of  cement  by  weight.     (See  §  85  in  this  con- 
nection.) 

ART.  16.     FINE  GRINDING 

89.  Effect  of  Fine  Grinding  on  the  Weight  of  Cement.  —  Fine 

grinding  will  decrease  the  weight  per  cubic  foot,  the  fine  ce- 
ment not  packing  as  closely  as  the  coarser  product.  In  "  Ce- 
ment for  Users,"  by  Mr.  Henry  Faija,  the  following  results  are 
given,  showing  the  relation  between  fineness,  weight,  and  spe- 


60 


CEMENT  AND  CONCRETE 


TABLE   16 
Relation   of  Fineness  to  Specific  Gravity  and  Weight  per  Bushel 

From  "  Cement  for  Users  " 


SAM- 
PLE. 

SPECIFIC  GRAVITY. 

WEIGHT  PER  BUSHEL. 

a 

b 

c 

a 

b 

c 

d 

e 

1 

3.00 

2.97 

3.07 

116.5 

107.5 

121.0 

112.0 

115 

2 

3.03 

2.94 

3.04 

116.0 

104.0 

130.5 

109.0 

115 

3 

3^02 

2.91 

3.035 

114.0 

100.0 

128.0 

104.5 

109 

cific  gravity:  (a),  cement  as  delivered;  (b),  sif tings  that  passed 
through  sieve  with  2,500  holes  per  sq.  in.;  (c),  coarse,  retained 
on  above  sieve;  (d),  cement  all  ground  to  pass  above  sieve;  (<?), 
coarse  particles  reground  to  pass  above  sieve. 

90.  Effect  of  Fine  Grinding  on  Time  of  Setting.  —  Since  the 
coarse  particles  of  cement  are  practically  inert,  there  is  every 
reason  to  believe  Uiat  finer  grinding  will  increase  the  activity 
of  a  sample,   since  it  will  render  some  inert  particles  active. 
For  the  reason  mentioned  in  §  81,  however,  it  is  difficult  to  show 
this  difference  in  time  of  setting  by  actual  tests. 

Tests  reported  by  Mr.  David  B.  Butler 1  showed  that  several 
Portland  cements  which  took  an  initial  set  in  20  to  30  minutes 
and  hard  set  in  45  to  120  minutes  would,  when  reground  to  pass 
a  sieve  having  180  meshes  per  linear  inch,  begin  to  set  in  from 
1  to  7  minutes  and  set  hard  in  5  to  15  minutes.  These  may  be 
considered  extreme  results;  the  rise  in  temperature  of  these 
cements  during  setting  was  so  great  as  to  indicate  they  were 
not  normal  cements,  and  variations  in  consistency  of  the  pastes 
may  have  influenced  the  time  of  setting. 

91.  EFFECT  OF  FINE  GRINDING  ON  STRENGTH.  —  Since  the 
best  burned  clinker  of  Portland  cement  is  the  hardest,  it  follows 
that  the  unground  particles  would,  if  ground  fine  enough  to 
become  active,  form  the  best  portion  of  the  cement.     This  is 
not,  a  priori,  true  of  natural  cements,  because  burning  renders 
some  varieties  of  cement  rock  softer  at  first,  but  when  the  burn- 
ing is  carried  beyond  a  certain  point  they  become  harder  again. 
The  coarse  particles  in  a  natural  cement  may  thus  be  either 


1  Proceedings  Inst.  C.  E.,  1898. 


FINE  GRINDING 


61 


from  underburned  or  overburned  rock;  hence  it  is  possible  that 
in  some  cases  it  might  be  better  to  leave  the  hardest  particles 
in  an  unground  state.  Thus,  while  it  has  been  generally  ac- 
cepted that  fine  grinding  improves  Portland  in  a  twofold  de- 
gree, —  by  bringing  into  action  the  best  burned  clinker,  as  well 
as  by  rendering  a  given  weight  of  cement  capable  of  coating  a 
larger  number  of  sand  grains,  —  a  similar  conclusion  concern- 
ing natural  cement  is  not  well  established. 

TABLE   17 

Effect  of  Fine  Grinding  of  Natural  Cement  on  the  Tensile 
Strength   of  Mortar 


REFERENCE. 
1 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

Neat 
Cement. 

1  Part  Stand- 
ard Sand 
to  1  Cement. 

2  Parts  Standard  Sand 
to  1  Cement. 

3  Parts 
Standard 
Sand  to  1  Ce- 
ment. 

4  Parts 
Standard 
Sand  to  1  Ce- 
ment. 

7  da. 

GJ  mo. 

7  da. 

28  da. 

28  da. 

3  mo. 

6  mo. 

2yr. 

6  mo. 

2yr. 

6  mo. 

2yr. 

a 

6 

c 

d 

e 

/ 

g 

h 

i 

J 

k 

I 

1 
2 

3 
4 

5 

268 
283 
278 
392 

538 
473 

538 
592 

224 

230 
307 
308 

381 

350 
433 
538 

207 
245 
292 
271 
21 

354 
433 
469 
344 

291 
426 
406 
369 
73 

70 
102 
92 
160 
45 

202 
302 
305 
274 

48 
65 
61 
110 

156 
212 
240 
205 

49 

78 
65 
90 

REFERENCE. 

FINENESS  OF  CEMENT, 
PER  CENT.  PASSING 
Sieve  Number. 

100 

120 

1.    Cement  as  received  passed  through  No.  20               76.5 
2.    Cement  as  received  passed  through  No.  100           100.0 
3.    Keground  in  mortar,  not  sifted      ....              9-3.8 

72.4 
94.6 
91.5 

Cement;  Natural,  Brand  Jn, 
No.  1.    Passing  No.  20  sieve. 
"     2.   Passing  No.  100  sieve. 
"     3.    Reground  before  sifting. 

"     4.    Particles  retained  on  No.  50  sieve,  reground  to  pass  No.  100  sieve, 
"    5.    Particles  retained  on  No.  50  sieve,  reground  to  pass  No.  50  sieve, 

but  retained  on  No.  100  sieve. 

All  briquets  made  by  one  molder  and  immersed  in  one  tank.     In  general, 
each  result  is  mean  of  five  specimens. 


62  CEMENT  AND  CONCRETE 

92.  Some  tests  bearing  upon  the  value  of  fine  grinding  have 
already  been  given  in  Table  15.     Samples  3  and  8  were  reground 
with  mortar  and  pestle  before  being  sifted.     If  we  compare  the 
results  given  by  sample  3  with  those  obtained  with  samples  1 
and  2,  not  reground,  it  appears  that  the  regrinding  diminishes 
the  strength  in  neat  mortars  but  increases  it  in  mortars  con- 
taining three   parts   sand  to   one   of   cement.     Regrinding   ap- 
pears to  be  no  better,  however,  than  sifting.     Comparing  sam- 
ple 8  with  samples  6  and  7,  it  is  seen  that  regrinding  Portland 
cement  does  not  diminish  the  strength  in  neat  mortars  to  the 
same  extent  as  sifting  does,   and  in  sand  mortars  regrinding 
generally  results  in  a  greater  increase  in  strength  than  sifting. 

93.  The   results   in   Table    17   were   obtained   with   another 
sample  of  natural  cement  and  are  of  greater  practical  value  as 
indicating  the  importance  of  fine  grinding,  since  in  these  tests 
a  sample  is  included  obtained  by  regrinding  the  original  cement 
without  previous  sifting.     The  conclusions  concerning  the  ce- 
ment retained  on  No.  50  sieve  reground  to  pass  No.  100,  and 
the  coarse  particles  alone  retained  between  sieves  50  and  100, 
are  practically  the  same  as  those  drawn  from  Table  13. 

As  to  the  other  three  samples,  the  No.  20  sieve  removed  only 
a  very  few  coarse  particles,  and  that  passing  this  sieve  may  be 
considered  to  represent  the  cement  as  received  The  No.  100 
sieve  removed  about  24  per  cent,  by  weight  from  the  original 
cement,  and  the  cement  that  was  reground  contained  but  about 
4  per  cent,  of  particles  which  would  not  have  passed  the  No. 
100  sieve.  The  third  sample,  reground  cement,  may  be  com- 
pared with  the  first  to  indicate  the  improvement  obtained  by 
finer  grinding,  and  it  may  be  compared  with  the  second  to  de- 
termine the  difference  between  removing  the  coarse  particles  by 
sifting  and  reducing  them  by  finer  grinding.  In  considering 
these  results  it  will  be  best  to  neglect  the  two-year  tests,  since 
all  of  the  samples  failed  at  this  age.  .  A  comparison  of  the  re- 
sults obtained  with  these  three  samples  indicates  that  while  the 
advantage  of  finer  grinding  is  not  apparent  in  neat  tests,  in 
sand  mortars  the  value  of  finer  grinding  is  more  marked  the 
larger  proportion  of  sand  used,  so  that  with  three  or  four  parts 
sand,  the  strength  with  the  fine  samples  is  about  50  per  cent, 
greater  than  with  the  cement  as  received.  It  also  appears  that 
the  reground  sample  gains  its  strength  more  rapidly  than  the 


FINE   GRINDING  63 

sifted  sample,  though  at  six  months  it  seems  to  make  little  dif- 
ference whether  the  coarse  particles  are  removed  by  sifting  or 
reduced  by  grinding. 

94.  Conclusions  as  to  the  Effect  of  Fine  Grinding  and  Sifting 
on  Tensile  Strength.  —  The  general   conclusions   to   be   drawn 
concerning  fine  grinding  and  sifting  may  be  summarized  as  fol- 
lows: According  to  the  tests  given,  it  appears  that  to  remove 
the  coarse  particles  from  a  sample  of  natural  cement  by  sifting, 
or  to  reduce  them  by  finer  grinding,  generally  diminishes  the 
strength  obtained  in  tests  of  neat  cement  mortars.     In  one-to- 
one   mortars,   the  strength  of  the  finer  samples   is   not   much 
greater  than  when  the  coarse  particles  are  present;  but  in  mor- 
tars containing  greater  proportions  of  sand,  the  advantage  ob- 
tained   by    eliminating    the    coarse    particles    is    very    marked 
in   the   case   of    natural   cement,   the   strength    given    by    the 
finer  samples  sometimes  exceeding  that  of  the  original  cement 
by  more  than  60  per  cent.     While  the  advantages  of   sifting 
and    finer   grinding  are  also   important  for   Portland   cements, 
there   does   not   result  such  a  large  proportionate  increase  in 
strength. 

Reground  samples  of  natural  cement  gain  strength  more 
rapidly  than  resifted  samples,  but  eventually  the  strength 
attained  is  about  the  same.  In  Portland  cements  regrinding 
seems  to  be  of  greater  value  than  resifting.  A  sample  of  natural 
cement  made  from  coarse  particles  reground  gains  strength 
rapidly,  and  for  mortars  with  small  proportions  of  sand,  gives 
good  results.  The  fact  that  such  samples  do  not  give  a  high 
strength  with  large  proportions  of  sand  is  doubtless  due  to  the 
fact  that  the  grinding  is  not  thorough,  and  the  indications  are 
that  the  material  of  which  such  coarse  particles  are  composed 
would  form  a  valuable  part  of  the  cement  if  ground  fine 
enough. 

The  coarse  particles  of  either  natural  or  Portland  cement 
may  be  replaced  by  grains  of  sand  of  the  same  size  without 
materially  affecting  the  strength  attained  by  neat  and  one-to- 
one  mortars,  but  for  mortars  containing  larger  proportions  of 
sand,  such  a  substitution  results  in  a  decreased  strength. 

95.  Finally,  it  may  be  said  that  the  process  of  manufacture 
and  the  character  of  the  materials  from  which  cement  is  made 
have  such  an  influence  on  the  relative  proportions  of  fine  and 


64  CEMENT  AND  CONCRETE 

coarse  particles  that  the  percentage  of  finest  particles  cannot 
be  determined  by  testing  with  a  coarse  sieve.  While  it  is  not 
known  at  what  point  of  fineness  grains  of  cement  begin  to  have 
cementitious  value,  or  what  proportion  of  the  cement  should  be 
the  finest  flocculent  matter,  it  is  certain  that  a  cement  should 
leave  as  small  a  percentage  as  possible  on  a  sieve  having  holes 
.004  inch  square,  in  order  to  have  the  greatest  sand  carrying 
capacity. 

There  is,  however,  a  reason  for  using  a  comparatively  coarse 
sieve  in  connection  with  the  fine  one.  Overburned  lime,  which 
is  likely  to  occur  in  Portland  cements,  is  more  dangerous  in  the 
form  of  coarse  particles  than  an  equal  quantity  in  a  fine  condi- 
tion, because  coarse  particles  slake  more  slowly  and  it  is  better 
that  expansion  should  occur  early  in  the  process  of  hardening 
if  it  is  to  occur  at  all.  For  the  same  reason  a  cement  that  would 
be  unsound  normally  may  be  rendered  less  dangerous  by  re- 
grinding. 

As  fine  grinding  is  expensive,  it  is  only  a  question  as  to  when 
the  increased  strength  obtained  is  offset  by  the  extra  expense 
incurred  in  grinding.  There  is  now  little  trouble  in  obtaining 
either  natural  or  Portland  cement  of  which  from  60  to  70  per 
cent,  will  pass  holes  .004  inch  square.  (See  §  79.) 


CHAPTER  VII 

TIME   OF   SETTING   AND   SOUNDNESS 

•  ART.  17.   SETTING  OF  CEMENT 

96.  Process  of  Setting.  —  When  cement  is  gaged  with  suffi- 
cient water  to  bring  it  to  a  paste,  and  is  then  left  undisturbed, 
it  soon  begins  to  lose  its  plasticity  and  finally  reaches  such  a 
condition  that  its  form  can  no  longer  be  changed  without  pro- 
ducing rupture.  This  change  of  condition  is  known  as  the 
"setting"  of  cement  and  is  considered  to  be,  in  a  measure,  dis- 
tinct from  " hardening."  Setting  usually  takes  place  within  a 
few  hours,  or  perhaps  minutes,  while  the  hardening  is  continu- 
ous for  months  or  years. 

The  precise  chemical  changes  that  take  place  in  the  setting 
and  hardening  of  cements  are  not  thoroughly  understood.  The 
chief  cementitious  ingredient  in  Portland  cement  is  considered 
to  be  a  tricalcium  silicate,  3  CaO,  SiO2;  in  contact  with  water  it 
forms  hydrated  monocalcic  silicate  and  calcium  hydrate.  This 
process  is  believed  to  contribute  more  to  the  final  hardening  of 
the  mortar  than  to  the  setting,  though  the  hydration  of  the 
finer  particles  of  this  important  compound  also  contributes  to 
the  first  setting.  It  is  considered  that  the  calcium  aluminates 
play  an  important  role  in  the  first  setting  of  cement,  as  they  set 
rapidly  in  contact  with  water,  and  it  has  been  suggested  that 
they  form  the  chief  active  constituents  of  natural  cement.1 

These  chemical  changes  cause  the  formation  of  crystals 
which  by  their  interlocking  and  adhesion  give  strength  to  the 
new  compounds.  For  a  scientific  and  detailed  treatment  of 
this  subject,  the  reader  is  referred  to  the  articles  of  M.  H.  Le 
Chatelier  in  Annales  des  Mines,  11,  pp.  413-465,  Trans.  Am. 
Inst.  Mining  Engineers,  August,  1893;  to  the  conclusions  of 
S.  B.  and  W.  B.  Newberry,  Cement  and  Engineering  News, 
1898;  and  to  "  The  Constitution  of  Portland  Cement  from  a 


1  S.  B.  Newberry,  "  Mineral  Resources  of  the  United  States,"  1892. 


66  CEMENT  AND  CONCRETE 

Fhysico-Chemical  Standpoint/'  a  paper  by  Mr.  Clifford  Richard- 
son read  before  the  Association  of  Portland  Cement  Manufac- 
turers at  Atlantic  City,  June  15,  1904,  Engineering  Record, 
August  13  and  20,  1904,  Engineering  News,  August  11,  1904. 

97.  THE  RATE  OF  SETTING  AND  ITS  DETERMINATION.  —  The 
setting  of  cement  being  a  gradual  and  continuous  process  with- 
out well-defined  points  of  change,  it  is  necessary,  in  order  to  com- 
pare the  rates  of  change  in  condition  of  different  samples,  to 
adopt  an  arbitrary  standard.     The  method  usually  adopted  is 
to  determine  the  resistance  of  the  mortar  to  the  penetration  of  a 
wire  or  needle.     The  wires  used   by  General   Totten   and  rec- 
ommended  by   General   Gilmore  for  this   purpose   are   now  in 
general  use  in  this  country.   One  of  the  wires  is  TV  inch  in  diame- 
ter and  is  loaded  to  weigh  |  pound;  the  other  is  J*  of  an  inch 
in  diameter  and  loaded  to  weigh  one  pound.     The  paste  is  said 
to  have  reached  " initial  set"  and  "end  of  set"  when  these  two 
wires,  respectively,  fail  to  make  an  impression  on  the  surface. 

98.  M.  Vicat  also  suggested  a  needle  test  as  follows:  The 
cement  paste  is  placed  in  a  conical  ring,  4  cm.  in  height  and  7 
cm.  in  diameter  at  the  base.     The  consistency  should  be  such 
that  a  rod  1  cm.  in  diameter  and  weighing  300  grams  does  not 
entirely   pierce   the   mass.     This   consistency   having   been   ob- 
tained by  trial,  a  needle  of  circular  cross-section  having  an  area 
of  1  sq.  mm.  and  loaded  to  weigh  300  grams,  is  gently  lowered 
on  the  paste.     The  moment  when  this  needle  no  longer  pene- 
trates the  mass  is  called  the  beginning  of  the  set,  and  the  time 
in  which  it  fails  to  make  an  impression  upon  it  is  called  the  end 
of  setting.     It  may  be  mentioned  in  passing,  that,  according  to 
a  few  comparative  tests  made  by  the  author,  when  a  cement 
paste  has  "set"  by  Gilmore's  "heavy"  wire,  ^  inch  weighing 
one  pound,  it  requires  about  1,100  grams  weight  on  the  Vicat 
1  sq.  mm.  needle  to  make  an  impression  on  the  paste.     Vicat's 
method  was  indorsed  by  the  Munich  Conference  and  was  sug- 
gested in  the  recent  progress  report  of  the  Committee  of  the 
American  Society  of  Civil  Engineers. 

99.  M.    LeChatelier   has    suggested    a    modification    of   this 
method  by  substituting  for  the  rod  1  cm.  in  diameter  a  disc  of  the 
same  diameter  carried  by  a  slender  rod,  the  disc  being  loaded 
to  weigh  50  grams,  the  normal  consistency  being  such  that  the 
disc  will  stop  midway  in  the  ring,  or  "vase."     The  beginning 


SETTING  OF  CEMENT  67 

and  end  of  setting  he  would  define  by  the  penetration  of  the 
needle  (1  sq.  mm.  in  section)  to  mid-depth  in  the  ring,  the 
weights  being  50  grams  and  3,000  grams,  respectively. 

100.  An  approximate  method  of  determining  time  of  setting 
is  also  in  use  as  follows:  After  mixing  the  cement  paste  to  the 
proper  consistency,  place  enough  of  it  on  a  glass  plate  to  form 
a  thin  cake,  or  "pat,"  about  three  inches  in  diameter  and  one- 
half  inch  thick  at  the  center,  thinning  toward  the  edges.     When 
the  pat  is  sufficiently  hard  to  bear  a  gentle  pressure  of  the  fin- 
ger nail,  the  cement  is  considered  to  have  begun  to  set,  and 
when  it  is  not  indented  by  a  considerable  pressure  of  the  thumb 
nail,  it  may  be  said  to  have  set. 

101.  Mr.   Henry   Faija  objected   to   all   methods   which    are 
based  upon  the  rates  of  acquiring  hardness,  on  the  ground  that 
there  are  periods  in  the  early  stages  of  hardening  that  may  be 
more  rationally  defined.     He  considers  that  the  time  at  which 
the  water  leaves  the  surface  of  the  pat,  depriving  it  of  its  glossy 
appearance,  is  really  the  beginning  of  setting,  and  that  this 
time  may  or  may  not  correspond  to  the  result  obtained  by  the 
use  of  the  needle. 

102.  Variations  in  the  Rate  of  Setting.  —  Some  of  the  quali- 
ties which  determine  the  actual  rate  of  setting  of  a  cement 
are,  its  composition,  degree  of  burning,  age  and  fineness.     Aside 
from  these  qualities  of  the  cement  itself,  the  addition  of  certain 
salts  subsequent  to  the  manufacture  also  influences  the  rate. 
The  observed  rate  of  setting  will  be  influenced  by  the  details 
of  the  test,  such  as  the  quantity,  temperature  and  composition 
of  the  water  used  in  gaging,  the  amount  of  gaging,  the  tem- 
perature of  the  cement,  and  the  temperature  and  character  of 
the  medium  in  which  the  pat  is  placed  after  molding. 

103.  An  over-limed  or  highly  limed  cement  is  usually  slower 
setting  than  an  over-clayed  one.     Among  natural  cements,  those 
of   the   aluminous   variety   are    usually   quick   setting.     Other 
things  being  equal,  a  well-burned  Portland  cement  will  be  slower 
setting  than  an  underburned  sample.     It  is  not  certain  that 
such  is  the  case  for  all  natural  cements,  though  it  probably  is 
true  of  most  of  them.     It  has  been  said  that  underburned  ce- 
ments owe  their  quick  setting  to  their  porosity,  but  the  forma- 
tion of  different  compounds  in  the  higher  temperature  may  also 
account  for  the  difference. 


CEMENT  AND  CONCRETE 


104.  The  effect  of  the  age  of  cement  on  its  time  of  setting 
is  very  marked,  but  varies  widely  with  different  samples.  The 
idea  that  cements  invariably  become  slower  setting  by  storage 
is  a  false  one.  The  origin  of  this  error  may  be  found  in  the 
fact  that  by  the  time  cement  has  reached  its  destination,  it 
has  usually  passed  through  the  earlier  and  more  rapid  changes 
in  characteristics.  Dr.  Erdmenger l  has  stated  that  some  Port- 
land cements  become  slower  setting,  while  some  set  more  rapidly 
as  a  result  of  storage.  Dr.  Tomei  made  experiments  on  several 
Portland  cements2  which  show  that  they  generally  become 
quicker  setting  at  first  (from  one  to  four  months  after  grind- 
ing), and  then  become  gradually  slower  setting,  until  at  the 
end  of  a  year  they  set  in  about  the  same  length  of  time  as 
when  fresh.  The  writer  has  seen  this  trait  exhibited  very 

TABLE    18 

Time  of  Setting  of  Five  Samples  of  Natural  Cement  as  Affected  by 

Aeration 


TIME  SETTING 

TIME  SETTING 

WATER. 

» 

CEMENT 

CEMENT  AERATED 

H 

FROM  PACKAGE. 

19  DAYS. 

5 

H 

w 

w 
_i 

PH 

42-3 

2 

^« 

£ 

8 

09 

1 

EFER 

M 

OS 

gc 

^ 

j* 

J 

Diff. 

& 

^ 

Diff. 
i-h. 

REMARKS. 

M 

PH  ^ 

1" 

g 

>-3 

1-3 

" 

^ 

£j 

5 

H-* 

^ 

i-T* 

H 

Min. 

Min. 

Min. 

Min. 

Min. 

Min. 

a 

6 

c 

a 

e 

/ 

9 

h 

j 

J 

1 

84  R 

32.0 

65° 

67  73° 

52 

110 

58 

54 

173 

119 

Five  samples, 

2 
3 

83  R 
82  R 

u 
(1 

' 

50 
44 

100 
100 

50 
56 

51 
48 

164 
166 

113 
118 

same  brand. 
Uj  and  O2  re- 
quired more 

4 

U2 

34.7 

60 

280 

220 

100 

326 

226 

and  less  wa- 

5 

6 

02 

84  R 

29.3 
40.0 

101 

87 

349 

1200 

248 
1110 

147 

130 

306 
1241 

159 
1111 

ter    respect- 
ively   than 
the  others  to 

7 

83  R 

ii 

80 

1178 

1098 

122 

1233 

1111 

make    same 

8 

82  R 

ii 

72 

1202 

1130 

125 

1227 

1102 

consistency. 

9 

U2 

42.7 

109 

1256 

1147 

202 

1221 

1019 

10 

02 

37.3 

192 

1247 

1045 

234 

1216 

982 

plainly  by  samples  of  Portland  cement  of  American  manufacture, 
but  has  not  noticed  it  in  natural  cements.  Table  18  gives  the 
results  of  some  tests  on  the  effect  of  aeration  on  the  time  of 


1  "Notes  on  Concrete,"  by  John  Newman,  p.  11. 
J  Trans.  A.  S.  C.  E..  Vol.  xxx,  p.  12. 


SETTING  OF  CEMENT 


69 


setting    of     five    samples    of    natural    cement   from   the   same 
factory. 

105.  The  coarse  particles  in  a  cement  retard  the  setting  be- 
cause they  are  inert.  Either  fine  grinding  or  sifting  will  doubt- 
less hasten  the  rate  of  setting,  but,  as  has  been  stated  above, 
the  detection  of  changes  in  the  rate  is  difficult.  Table  11, 
§  81,  gives  the  results  of  a  few  tests  on  this  subject. 

106.  Addition  of  Salts.  —  The  time  of  setting  of  a  cement  is 
sometimes  regulated  at  the  factory  by  addition  of  sulphate  of 
lime  to  the  finished  product.  Such  additions  are  admitted  to 
the  extent  of  two  per  cent,  by  the  regulations  of  the  Asso- 
ciation of  German  Portland  Cement  Makers,  and  are  now  quite 
generally  made  by  American  Portland  cement  manufacturers. 
Table  19  gives  the  results  of  a  few  experiments  on  the  effect 
of  plaster  of  Paris  on  the  time  of  setting  of  several  cements. 

TABLE   19 
Effect  of  Plaster  Paris  on  Time  of  Setting 


a~ 

Time  to  Bear  \  Ib. 

Time  to  Bear  1  Ib. 

Q  s  .2 

Wire,  Minutes,  with  Plaster 

Wire,  Minutes,  with  Plaster 

CEMENT. 

'"  *  e{ 

Paris  as  Certain  Percent- 

Paris as  Certain  Percent- 

|jj 

age  of  Cement  and 
Plaster  Paris. 

age  of  Cement  and 
Plaster  Paris. 

Kind. 

Brand. 

|is 

0% 

1% 

2% 

3% 

6% 

0% 

1% 

2% 

3% 

6% 

Portland 

s 

24 

232 

477 

460 

425 

40 

498 

917 

910 

860 

832 

u 

R 

24 

96 

375 

381 

358 

75 

345 

745 

776 

778 

750 

l( 

X 

26 

4 

258 

287 

268 

84 

305 

625 

725 

668 

694 

Natural 

Gn 

34 

38 

106 

107 

86 

42 

543 

414 

527 

671 

632 

" 

An 

34 

93 

179 

302 

295 

93 

193 

439 

592 

726 

698 

It  is  seen  that  small  percentages  retard  the  initial  setting  in 
a  marked  degree,  the  maximum  effect  usually  being  given  by 
2  per  cent,  of  the  plaster.  Larger  percentages  tend  to  make 
the  cement  quicker  setting  again,  so  that  with  6  to  10  per  cent, 
added,  the  cement  may  begin  to  set  quicker  than  without  the 
addition  of  plaster.  The  final  set  (time  to  bear  one  pound 
wire)  does  not  appear  to  be  thus  hastened  by  large  percentages. 
This  might  be  considered  to  indicate  that  the  hastening  of  the 
initial  set  is  caused  by  plaster  of  Paris  taking  up  the  water  from 
the  cement  and  obtaining  sufficient  hardness  to  bear  the  light 
wire. 

The  probable  explanation  of  the  action  of  a  small  amount  of 


70  CEMENT  AND  CONCRETE 

sulphate  of  lime  in  retarding  the  setting  is  that  suggested  by 
M.  Candlot, l  namely,  that  the  aluminate  of  lime,  to  which  is 
due  the  initial  setting,  dissolves  less  readily  in  a  solution  of 
sulphate  of  lime  than  in  pure  water.  If  the  aluminate  does 
not  commence  to  hydrate  until  the  silicate  of  lime  has  set,  the 
subsequent  combination  of  the  sulphate  and  aluminate  may 
cause  the  mortar  to  disintegrate. 

107.  Solutions  of  common  salt  have  been  found  to  retard 
the  setting,  but  when  a  large  percentage  of  salt  is  used,  it  some- 
times forms  a  crust  on  the  top  which  may  resist  a  light  wire  and 
thus  make  the  paste  appear  to  be  quicker  setting.  Sea  water 
generally  retards  the  setting  somewhat  more  than  solutions  of 
common  salt,  probably  on  account  of  the  magnesian  salts  pres- 
ent, but  M.  Candlot  says  that  cements  to  which  sulphate  of 
lime  has  been  added  set  more  rapidly  when  gaged  with  sea  water 
than  when  gaged  with  fresh  water. 

The  effect  of  calcium  chloride  on  the  setting  of  cements  is 
entered  into  in  detail  in  M.  Candlot's  treatise  on  "  Cements  and 
Hydraulic  Limes,"  and  may  be  summarized  as  follows:  A  weak 
solution  of  calcium  chloride  renders  Portland  cement  slower 
setting  because  the  aluminate  of  lime  dissolves  more  slowly  in 
such  a  solution  than  in  pure  water.  On  the  other  hand,  the 
aluminate  dissolves  rapidly  in  a  concentrated  solution  of  calcium 
chloride,  and  therefore  such  a  solution  hastens  the  setting  of 
Portland  cement.  Aluminous  cements,  i.e.,  cements  containing 
a  very  high  percentage  of  alumina,  are  not  appreciably  affected 
by  gaging  with  a  comparatively  weak  solution  of  calcium  chlo- 
ride on  account  of  the  large  excess  of  aluminate  of  lime  present; 
and  on  the  other  hand,  cements  containing  no  alumina  are  not 
affected,  as  in  such  cements  the  hardening  is  due  to  the  silicate 
of  lime.  A  weak  solution  of  the  chloride  hastens  the  hydration 
of  the  free  lime,  and  therefore  a  cement  which  contains  a  dan- 
gerous percentage  of  the  latter  may  be  made  sound  by  gaging 
with  such  a  solution,  as  the  lime  may  thus  be  hydrated  before 
the  cement  sets.  The  chloride  of  calcium  test  for  soundness  is 
based  on  the  supposition  that  the  free  lime  may  be  hydrated  by 
the  action  of  the  chloride  soon  after  the  setting  of  the  cement, 
and  thus  the  expansive  action  be  hastened. 


"Ciments  et  Chaux  Hydrauliques,"  par  E.  Candlot, 


SETTING  OF  CEMENT 


71 


The  effect  of  sugar  on  the  time  of  setting  does  not  seem  to 
be  well  known,  but  it  is  said  l  that  the  presence  of  saccharine 
matter  may  either  accelerate  or  retard  the  setting  of  the  cement, 
depending  on  the  amount  of  sugar  present,  the  character  of  the 
cement  and  the  amount  of  water  used. 

108.  The  quantity  of  water  used  in  gaging  has  a  most  impor- 
tant influence  on  the  test  for  time  of  setting,  an  increased  quan- 
tity of  water  retarding  the  setting.  This  may  be  seen  from 
Table  20. 

TABLE   20 
Effect  of  Consistency  of  Mortar  on  the  Time  of  Setting 


'    Water    as    per  cent,    of 

J    H 

cement  by  weight    .     . 

26.7 

2K.O 

30.8   33.3 

36.4 

40.0 

gs. 

Minutes  to  bear  -/>  inch 

H    * 

wire  weighing  \  pound. 

20 

2;> 

30 

42 

4(5 

55 

£& 

Minutes  to  bear  ^T  inch 

wire  weighing  1  pound 

28 

41 

57 

76 

78 

85 

Water   as    per    cent,    of 

a 

»    H 

cement  by  weight    . 

24 

26 

28 

30 

32 

34 

36 

ll« 

Minutes  to  bear  y1,  inch 

§| 

\  pound  wire      .     .     . 

2 

2 

3 

~7 

21 

28 

38 

£Q 

Minutes  to  bear  ^  inch 

1  pound  wire    . 

160 

188 

279 

289 

371 

403 

583 

As  might  be  supposed,  this  influence  varies  with  different 
samples,  and  M.  H.  LeChatelier 2  has  given  the  following  table 
which  illustrates  this  point. 

TABLE    21 

Effect  of  Consistency  of  Mortar  on  Time  of  Setting 


CEMEXT. 

PEK  CtfXT. 
WATEK. 

TIME  SKTTIXG, 
Minutes. 

Portland  A                                                    J 

24 

20 

Portland  B        .                                               \ 

34 
25 

85 

7 

Quick  settin0"  Vassy                                 .    < 

35 

50 

45 
5 

58 

10 

"Masonry  Construction/'  I.  O.  Baker,  p.  98. 
2  "Tests  of  Hydr.  Materials,"  p.  33. 


72 


CEMENT  AND  CONCRETE 


109.  It  is  necessary,   then,  in  writing  specifications  and  in 
making  tests,  where  the  time  of  setting  is  at  all  carefully  con- 
sidered, to  note  the  consistency  of  the  paste  used  in  the  test. 
Practically,  it  is  preferable  to  use  a  paste  rather  thinner  than 
that  usually  employed  for  briquets. 

The  consistency  is  sometimes  defined  by  M.  Vicat's  apparatus 
of  a  rod  1  cm.  in  diameter,  or  by  M.  LeChatelier's  modification 
of  the  same  mentioned  above,  or  by  the  requirement  that  it 
shall  be  at  the  point  of  ceasing  to  adhere  to  the  trowel.  Another 
definition  is  that  it  shall,  when  placed  on  a  glass  plate,  flow 
toward  the  edges  only  on  repeated  jarring  of  the  plate.  This 
last  is  a  very  fair  approximate  method,  though  giving  a  rather 
thin  paste. 

That  mortars  set  more  slowly  than  neat  cement  paste  is 
largely  due  to  the  increased  amount  of  water  present  in  the 
former,  this  excess  of  water  being  required  to  moisten  the 
grains  of  sand.  The  relation  between  the  time  of  setting  of  mor- 
tars and  neat  cement  paste  is  not  definite.  M.  Candlot  found 
the  time  of  setting  of  one-to-three  mortars  to  be  from  two  to 
twenty  times  as  great  as  that  of  the  paste  of  neat  cement  of 
normal  composition. 

110.  The  temperature  of  the  cement  and  water  also  has  an 
important  bearing  on   the   observed   time   of  setting.     As   the 
temperature  of  the  materials  is  increased,  the  time  of  setting 
diminishes  in  about  the  same  proportion.     The  following  table 
gives  a  few  of  the  results  obtained  by  M.  Candlot  *  with  Port- 
land cements. 

TABLE   22 

Effect  of  Temperature  of  Materials  on  Time  of  Setting 


TEMPERATURE, 
Degrees  C. 

TIME  OF  SETTING, 
Minutes. 

C611161lt  No     1                   \ 

6 
15 

60 

25 

Cement  No.  2  ] 

25 

7 
20 

4 

350 

295 

30 

190 

Table  23  gives  the  results  of  similar  tests  made  under  the 
author's    direction.     The    temperatures    of    cement   and    water 


fdments  et  Chanx  Hydrauliques,f>  par  E.  Candlot. 


SETTING  OF  CEMENT 


73 


were  varied  while  the  temperature  of  the  room  in  which  the 
tests  were  made  remained  nearly  constant,  or  from  63°  to  67° 
Fahr. 

TABLE   23 

Effect    of    Temperatures   of    Cement    and    Water    on   the    Time   of 

Setting  of  Paste 


Temp,  cement  and  water,  | 
Degrees,  Fahr.                 .  ) 

40 

50 

60 

70 

80 

90 

100 

110 

Minutes  to  bear  ,-L  } 

inch  wire  weigh-  >  Portland 

270 

247 

225 

196 

175 

158 

135 

.  .  . 

ing  *  pound.         }  Nat,urai 

102 

90 

84 

72 

60 

54 

55 

43 

111.  Amount  of  Gaging.  —  If  a  cement   paste  containing  a 
moderate  amount  of  water  be  insufficiently  gaged,  it  will  appear 
dry,   when   a   more  thorough   working   might   make  it   plastic. 
Thus  an  insufficient  gaging  may  make  a  cement  appear  quicker 
setting.     It  is  also  the  case  that  when  a  cement  is  regaged  after 
having  begun  to  set,  the  second  setting  will  take  place  more 
slowly;  this,  however,  is  a  somewhat  different  matter. 

112.  The  temperature  and  character  of  the  medium  in  which 
the  pat  is  kept  during  the  setting  process  will  have  a  decided 
influence  on  the  rate  of  setting. 

This  is  clearly  shown  by  the  following  table,  given  by  M. 

TABLE   24 

Time  of   Setting  as  Affected  by  Temperature  of  the  Water  and 
of  the  Medium  in  which  Cement  Sets 


SAMPLE. 

TEMPERATURE 

TIME  REQUIRED  TO 

Of  water  at  time 
of  gaging. 

Of  air  during 
setting. 

Begin  to  set. 

Set. 

Degrees  C. 

Degrees  C. 

Hr.      Min. 

Hr.      Min. 

1     I 

0 
16 

1 

16 

6         47 
0         20 

11             0 
2  .       23 

2     { 

0 
16 

1 
16 

5         30 
0         52 

8          8 
6        l:i 

3     1 

0 
15 

3 

15 

12           0 
0         43 

20          0 
3          3 

*     1 

0 
15 

3.5 
17 

0         24 
0        20 

1          3 
0        45 

74  CEMENT  AND  CONCRETE 

Paul  Alexandre,1  from  which  it  appears  that  different  samples 
are  affected  in  very  different  degrees.  It  is  seen  that  the 
higher  the  temperature,  the  more  rapid  the  setting. 

113.  At  temperatures  below  32°  F.    (0°  C.),  setting   seems 
to  be  entirely  suspended.     If  a  cement  paste,  which  has  been 
submitted   to  such   low  temperatures  since  gaging,  is  brought 
into  a   warm   room,  the  setting  process  begins  as  though  the 
mortar   had    just    been    gaged.      It   must   not   be    concluded, 
however,   that  freezing  has   no  evil   effect  on  mortars.      (See 
Art.  50.) 

114.  Setting  in  Air  and  Water.  —  A  cement  paste  sets   much 
quicker  in  air  than  in  water.     This  is  due  to  the  percolation  of 
water  to  the  interior  of  the  pat,  when  it  is  immersed  as  soon  as 
made,  being  analogous  to  using  an  excess  of   water   in  gaging. 
When  a  pat  sets  in  dry  air,  the  evaporation  of  water  from  the 
surface  hastens  the  hardening  of  that  portion.     If  immersed 
directly  after  it  has  set  in  air,  it  re-softens,  and  this  is  also 
true  of  some  briquets  immersed  when  twenty-four  hours  old. 
The  time  of  setting  of  cements  that  are  to  be  deposited  under 
water  may  well  be  tested  in  that  medium,  when  they  should 
be  protected  by  a  mold  of  some  form  to  retain  their  shape. 
Ordinarily  the  time  of  setting  should  be  tested  in  moist  air. 

Cements  are  said  to  set  more  quickly  in  compressed  air  than 
in  free  air;  this  may  be  partially  due  to  the  higher  temperature 
usually  existing  in  the  former. 

115.  Requirements  as  to  Time  of  Setting.  —  What  is   desir- 
able as  to  time  of  setting  will,  of  course,  depend  on  the  work 
in  hand;  certain  purposes  requiring  that  the  cement  shall  be 
able  to  retain  its  shape  soon  after  deposition,  while  in  other 
cases  ability  to  mix  large  quantities  at  a  time,  without  fear  of 
the  cement  setting  before  it  is  in  place,  may  be  very  convenient. 
An  extremely  quick  setting  cement  should  be  regarded  with 
suspicion  until  it  has  proved  itself  of  good  quality.     It  is  some- 
times stated  that  where  a  quick  setting  mortar  is  desired,  nat- 
ural cement  must  be  used,  but  this  is  not  true;  either  Portland 
or  natural  may  be  found  with  almost  any  rate  of  setting  de- 
sired.    As  a  general  rule,  however,  among  cements  that  have 
been  stored  several  months,  the  Portlands  are  slower  setting. 

1  "Recherches  Experimentales  sur  les  Mortiers  Hydrauliques,"  par  Paul 
Alexandre. 


SETTING  OF  CEMENT  75 

Portland  cement  will  ordinarily  begin  to  set  in  from  twenty 
minutes  to  six  hours,  and  natural  cement  in  from  ten  minutes  to 
two  hours,  though  there  are  many  cements  the  time  of  setting  of 
which  is  outside  of  these  limits. 

116.  Conclusions.  —  The  purpose  aimed  at  in  the  test  for 
time  of  setting  will,  to  a  certain  extent,  regulate  the  method 
to  be  employed.  The  pressure  of  the  finger  nail  will  be  suf- 
ficient to  determine  (after  a  little  experience)  whether  a  cement 
will  answer  a  certain  purpose  in  this  regard.  •  But,  if  one  is 
working  to  rigid  specifications,  or  pursuing  investigations  as  to 
the  effect  of  different  treatment  on  time  of  setting,  it  becomes 
very  desirable  to  have  a  method  of  determining  and  defining 
the  consistency  of  the  mortar,  and  an  accurate  method  of  de- 
termining the  rate  of  setting. 

In  the  author's  experience,  the  Vicat  consistency  apparatus 
as  modified  by  M.  LeChatelier  (see  §  99)  has  proved  unsatisfac- 
tory except  for  thin  pastes  of  neat  cement  or  mortars  contain- 
ing less  than  two  parts  of  sand.  If  the  paste  is  not  of  such  a 
consistency  as  to  run  freely  into  the  ring,  or  "vase,"  an  error 
may  be  introduced  in  the  method  of  filling  the  latter.  In  oper- 
ating with  a  natural  cement  it  was  found  that  a  neat  paste,  in 
which  the  water  used  was  32  per  cent,  of  the  dry  cement,  re- 
quired a  gross  weight  of  640  grams  to  make  the  disc  (1cm.  diam- 
eter) penetrate  midway  in  the  vase;  with  33  per  cent,  water, 
a  weight  of  410  grams  was  required;  34  per  cent.,  about  250 
grams;  35  per  cent.,  175  grams;  37  per  cent.,  155  grams.  It 
would  seem  that  some  modification  of  this  apparatus  might  be 
made  which  would  not  only  indicate  when  a  thin,  neat  cement 
paste  has  the  assumed  "normal"  consistency,  but  which  would 
also  define  the  consistency  of  a  given  mortar,  whether  of  neat 
cement  or  of  sand  mixture. 

General  Gilmore's  wires  are  very  simple,  and  will  perhaps 
answer  the  purpose  of  obtaining  the  time  of  setting  as  well  as 
any  method  in  use.  They  can  be  used  somewhat  more  accu- 
rately if  the  wires  are  made  to  slide  vertically  in  a  frame,  than 
when  held  in  the  hand. 

The  necessity  of  care  in  all  of  the  details  of  this  test,  tem- 
perature and  amount  of  water,  amount  of  gaging,  character 
of  medium,  etc.,  has  been  sufficiently  emphasized  in  the  preced- 
ing paragraphs. 


76  CEMENT  AND  CONCRETE 

ART.  18.     CONSTANCY  OF  VOLUME 

117.  That  a   cement   should   not    contain  within  itself  ele- 
ments which  may  lead  to  its  destruction,  is  evidently  a  most 
important  quality.     It  is  probable  that  nearly  all  cements  un- 
dergo a  slight  change  in  volume  during  induration,  contracting 
in  air  and  expanding  in  water.     But  it  is  the  detection  of  those 
larger  changes,  which  result  from  bad  proportions  or  defective 
manufacture,  and  which  cause  deterioration  or  even  complete 
disintegration,  that  is  the  object  of  the  tests  for  soundness. 

118.  Causes  of  Unsoundness.  —  The  most  frequent   cause  of 
unsoundness  is  considered  to  be  the  presence  of  free  lime  or 
magnesia.     (See  §§49  and  50.)     Any  one  of  the  following  causes 
may  account  for  the  presence  of  free  lime  in  cement:  (1)  An 
excessive  percentage  of  lime  may  have  been  used  in  proportion- 
ing the  raw  materials;  (2)  the  raw  materials  may  not  have  been 
sufficiently   mixed  to  render  the  mass  homogeneous;  (3)   hard 
particles  of  lime,  such  as  shells,  may  not  have  been  ground  fine 
enough  in  making  the  mix  to  permit  them  to  enter  into  com- 
bination with  the  other  ingredients  during  burning;  or  (4)  the 
cement  may  have  been  underburned,  so  that  part  of  the  lime 
did  not  enter  into  combination. 

The  particles  of  free  lime  which  occur  in  cements  are  nat- 
urally rather  difficult  to  slake  on  account  of  their  impurity  and 
the  high  temperature  at  which  they  have  been  calcined,  and 
the  same  thing  is  probably  true  of  magnesia.  It  may  thus 
require  weeks  or  months  of  exposure  to  the  atmosphere  to  cor- 
rect tendencies  to  expand  due  to  the  presence  of  free  lime  or 
magnesia.  Likewise  when  such  defective  cements  are  immersed 
in  water  of  ordinary  temperature,  the  expansion  may  not  occur 
for  a  considerable  period.  This  fact  has  led  to  the  use  of  hot 
tests  of  various  kinds  to  detect  such  faults,  but  before  touch- 
ing on  these  so-called  " accelerated  tests/7  the  ordinary  cold- 
water  test  will  be  described. 

119.  TESTS  FOR  SOUNDNESS.—  The  Committee  of  the  Amer- 
ican  Society   of   Civil   Engineers   on   a   "  Uniform   System   for 
Tests  of  Cement"  recommended,  in  1885,  the  following  test  for 
soundness:  "Make  two  cakes  of  neat  cement  two  or  three  inches 
in  diameter,  about  one-half  inch  thick,  with  thin  edges.     One 
of  these  cakes,  when  hard  enough,  should  be  put  in  water  and 


CONSTANCY  OF   VOLUME  77 

examined  from  day  to  day  to  see  if  it  becomes  contorted,  or  if 
cracks  show  themselves  at  the  edges,  such  contortions  or  cracks 
indicating  that  the  cement  is  unfit  for  use  at  that  time.  In 
some  cases  the  tendency  to  crack,  if  caused  by  the  presence,  of 
too  much  unslaked  lime,  will  disappear  with  age.  The  re- 
maining cake  should  be  kept  in  air  and  its  color  observed,  which 
for  a  good  cement  should  be  uniform  throughout,  yellowish 
blotches  indicating  a  poor  quality;  the  Portland  cements  being 
of  a  bluish-gray,  and  the  natural  cements  being  light  or  dark, 
according  to  the  character  of  the  rock  of  which  they  are  made." 
For  the  ordinary  cold  test  this  method  will  probably  give  as 
valuable  results  as  any  of  the  forms  that  are  suggested. 

120.  The   German  regulations  require  a  very  similar    test, 
except  that  in  the  case  of  slow  setting  cements  the  pat  is  not 
immersed  until  twenty-four  hours  old.     While  a  cement  that  is 
decidedly  bad  may  show  its  defects  in  from  one  day  to  one  week 
by  this  cold  water  test,  it  may  be  the  case  that  cracks  will  ap- 
pear only   after  several  months'   immersion.     It  has  therefore 
been   proposed   to   hasten   the   destructive   action   of   the   free 
lime  or  magnesia  by  submitting  the  cakes  of  cement  to  steam, 
hot  water,  or  dry  heat. 

121.  The  Kiln  Test,  recommended  by  Prof.  Tetmajer  in  1890, 
consists  in  placing  in  an  air  bath,  pats  which  have  been  kept 
in  moist  air  for  twenty-four  hours;  and  then  gradually  raising 
the  temperature  of  the  air  bath  to  120°  C.     This  temperature 
is  maintained  for  at  least  one-half  hour  after  the  disengage- 
ment of  steam  has  ceased.     The  pats  should  show  no  tendency 
to  expand  under  this  treatment,  but  if  cements  fail  to  pass  the 
test,  the  results  of  the  ordinary  cold  water  treatment  are  to  be 
awaited.     This   test  is   intended   for   cements   that   are   to   be 
used  in  air. 

122.  The  Boiling  Test,  which  was  also  recommended  by  Prof. 
Tetmajer,  consists  in  placing  the  pats,  twenty-four  hours  after 
made,  in  water  of  ordinary  temperature,  and  gradually  heating 
the  water  to  bring  it  to  the  boiling  point  in  about  an  hour; 
five  or  six  hours  in  the  boiling  water  should  develop  no  defects. 
This  is  a  severe  test,  and  has  been  objected  to  on  the  ground 
that  cements  which  have  been  well  proportioned,  but  which 
are  a  trifle  underburned,  will  fail  to  pass  this  test  while  giving 
good  results. in  mortars  to  be  used  in  the  air,     This  test,  how- 


78  CEMENT  AND  CONCRETE 

ever,  is  steadily  gaining  in  favor,  and  is  used  in  many  cement 
works  as  a  test  of  quality. 

123.  The  Warm  Water  Test.  —  Mr.  H.  Faija  was    an  early 
experimenter  in  accelerated  tests  for  soundness,  and  about  1882 
he  began  the  use  of  a  "steamer,"  using  a  temperature  of  about 
110°  Fahr.     After  eleven  years'  use  he  still  believed  this  tem- 
perature to  be  high  enough  to  detect  tendencies  to  expand  in 
faulty  cements.     The  apparatus1  "consists  of  two  vessels,  one 
within  the  other,  a  water  space  being  thus  maintained  between 
them,  which  assists  in  equalizing  the  temperature  of  the  inner 
or  working  vessel."     The  latter  is    partially  filled  with  water 
and  is  provided  with  a  rack  or  shelf  near  the  top.     A  ther- 
mometer is  inserted  through  the  cover  of  the  inner  vessel,  and 
the  water  within  is  kept  constantly  at  110°  Fahr.     As  soon  as 
the  pat  is  gaged,  it   is  placed  on  the  rack  in  the  vapor,  which 
will  be  at  about  100°  Fahr.     After  six  or  seven  hours  in  this 
moist  heat,  the  pat  is  immersed  in  the  warm  water.     "In  the 
course  of  twenty-four  hours  it  is  taken  out  and  examined,  and  if 
then  found  to  be  quite  hard  and  firmly  attached  to  the  glass,  the 
cement  may  at  once  be  pronounced  sound  and  perfectly  safe 
to  use;  if,  however,  the  pat  has  come  off  the  glass  and  shows 
cracks  or  friability  on  the  edges,  or  is  much  curved  on  the 
under  side,  it  may  at  once  be  decided  that  the  cement  in  its 
present  condition  is  not  fit  for  use."     Mr.  Faija  also  recom- 
mended, in  case  of  failure  in  the  first  test,  that  the  cement  be 
spread  out  in  a  thin  layer  for  a  few  days  and  a  second  test 
made.     If  the  cement  passes  this  second  test,  it  is  pronounced 
sound  and  fit  for  use  after  being  stored  a  sufficient  length  of 
time. 

124.  The  Hot  Water  Test.  —  The  temperature  to  be  used  in 
accelerated  tests  for  soundness  is  a  point  which  has  received 
much  attention  and  is  still  under  discussion.     In  1890  M.  Deval 
described  a  series  of  experiments  he  had  made,  in  which  he 
employed  a  temperature  of  80°  C.     While  this  is  much  more 
severe  than  the  temperature  used  by  Mr.  Faija,  it  is  still  mild 
in  comparison  to  some  temperatures  that  have  been  advocated. 

125.  Mr.  W.  W.  Maclay,  who  was  probably  the  first  engi- 
neer in  this  country  to  introduce  a  hot  test  requirement  in 


1  "Portland  Cement  Testing,"  by  H,  Faija,  Trans,  A,  S.  C.  E.,  Vol.  xvii, 
p.  222. 


CONSTANCY  OF   VOLUME  79 

specifications,  gave  the  results  of  his  experiments  in  a  paper 
presented  to  the  American  Society  of  Civil  Engineers  in  1892. 
The  method  used  "  consists  in  molding  six  pats  of  pure  cement 
and  water,  about  one-half  inch  thick  and  about  three  inches  in 
diameter,  on  thin  glass  plates,  and  of  the  same  consistency  as 
for  the  briquets  for  tensile  strength."  The  treatment  to  which 
these  pats  are  submitted  is  as  follows:  - 

No.  1,  in  steam  (vapor)  bath,  temperature  195°  to  200°  F., 
as  soon  as  made. 

No.  2,  in  same  vapor  bath  when  set  hard  (bear  Jf  inch  wire 
weighing  one  pound). 

No.  3,  ditto,  after  twice  the  length  of  time  in  air  allowed  the 
second  pat. 

No.  4,  ditto,  after  24  hours. 

No.  5,  in  water  of  temperature  about  60°  F.  when  set  hard. 

No.  6,  kept  in  moist  air  at  temperature  of  about  60°  I£. 

"The  first  four  pats  are  each  kept  in  the  steam  bath  three 
hours,  then  immersed  in  water  of  a  temperature  of  about  200° 
Fahr.  for  twenty-one  hours  each,  when  they  are  taken  out  and 
examined.  To  pass  this  test  perfectly,  all  four  pats,  after  being 
twenty-one  hours  in  hot  water,  should,  upon  examination,  show* 
no  swelling,  cracks,  nor  distortions,  and  should  adhere  to  the 
glass  plates.  The  latter  requirement,  while  it  obtains  with 
some  cements  nearly  free  from  uncombined  lime,  is  not  insisted 
upon;  the  cracking,  swelling  and  distortion  of  the  pats  being 
much  the  more  important  features  of  this  test.  The  cracking 
or  swelling  of  No.  1  pat  alone  can  generally  be  disregarded." 

126.  DevaPs  Method.  —  Making  tests  of  mortar  briquets, 
which  have  been  kept  in  hot  water,  seems  to  be  the  most  rational 
accelerated  test  for  soundness.  This  method  was  used  in  Ger- 
many several  years  ago,  when  it  was  claimed  that  a  definite 
relation  existed  between  the  results  thus  obtained  and  the  longer 
time  cold  water  tests.  This  theory  being  disproved,  threw  dis- 
credit on  the  hot  test,  but  M.  Deval l  has  since  made  many 
experiments  showing  that  it  is  of  much  value  in  detecting 
bad  products. 

The  method  consists  in  making  briquets  with  three  parts 
sand  to  one  of  cement,  and  after  twenty-four  to  seventy-two 

1  "  Hot  Tests  for  Hydraulic  Cements,"  M.  Deval,  Bull.  Soc.  d' Encourage- 
ment, etc.,  1890,  pp.  560-583. 


80 


CEMENT  AND  CONCRETE 


hours  in  moist  air,  according  to  the  rate  of  setting,  immersing 
them  in  water  maintained  at  80°  C.,  the  briquets  being  broken 
after  an  immersion  of  from  two  to  seven  days.  These  hot 
water  briquets  are  to  be  compared  with  briquets  stored  in 
water  of  the  ordinary  temperature  and  broken  at  seven  and 
twenty-eight  days  after  immersion. 

127.    Among  other  tests  M.  Deval  compared   the  results  ob- 
tained with  six  samples  of  Portland  cement  as  follows:  — 
No.  1.    Good  finely  ground  cement  of  modern  make. 
No.  2.    Coarsely  ground  cement  of  good  quality,  but  partially 

aerated. 
No.  3.    Quick  setting  cement  with  low  per  cent,  lime  and 

lighter  burn. 

No.  4.    Made  from  clinker  having  property  of  disintegrating 
spontaneously  while  cooling;  large  proportion  of  inert 
m  material. 

No.  5.    Under-burnt  cement;  contains  free  lime. 
No.  6.    Over-limed  cement. 
The  results  of  the  tests  are  given  in  the  following  table:  — 


TABLE  25 

Cold  and  Hot  Tests  on  Six  Samples  of  Portland  Cement 
(M.  Deval) 


TENSILE  STRENGTH  IN  KILOS  PER  SQ.  CM. 

CEMENT. 

Cold. 

Hot. 

7  days. 

28  days. 

2  days. 

7  days. 

1 

15.0 

23.3 

17.2 

24.3 

2 

6.7 

13.7 

7.6 

11.0 

3 

6.2 

16.5 

7.3 

16.2 

4 

2.9 

3.9 

) 

5 

6.1 

12.2 

Disintegrated. 

6 

7.6 

20.2 

5 

No.  4,  when  allowed  forty-eight  hours  to  set,  gave  3.2  kilos 
at  two  days,  and  4.3  kilos  at  seven  days,  when  tested  hot. 
Among  the  cements  which  disintegrated  in  the  hot  water,  the 
only  one  that  gave  a  high  result  cold  was  No.  6,  and  this  sam- 
ple, it  is  stated,  would  crack  and  swell  badly  even  in  cold  water 


CONSTANCY  OF   VOLUME  81 

if  mixed  neat.  It  is  quite  possible,  however,  that  a  sample 
might  be  found  which,  not  having  quite  as  flagrant  defects  as 
No.  6,  would  pass  all  the  cold  tests  but  be  condemned  by  the 
hot  test. 

128.  The   conclusions   drawn    from  these  experiments  have 
been  stated  as  follows:  — 

"(1)  Tests  made  cold  do  not  indicate  the  quality  of  the 
cement,  inasmuch  as  cement  containing  excess  of  lime,  and,  in 
consequence,  deplorably  bad,  may  give  excellent  results." 

"(2)  Portland  cement  of  good  quality,  mixed  with  normal 
sand  in  the  proportion  of  one  to  three,  resists  water  at  80°  C. 
Its  strength  at  two  and  seven  days  after  setting  is  about  equal 
to  that  which  it  would  have  at  seven  and  twenty-eight  days 
in  the  cold." 

"(3}  Poor  cement  containing  much  inert  material  does  not 
resist  the  action  of  water  at  80°  C.  unless  the  setting  be  allowed 
to  proceed  for  some  days  before  immersion." 

"(4)  Cements  containing  free  lime  do  not  withstand  the  ac- 
tion of  water  at  80°  C.  if  immersed  twenty-four  hours  after 
setting."  Comparison  of  the  strength  hot  and  cold  will  suffice 
for  the  detection  of  even  small  quantities  of  free  lime. 

129.  Before  passing  to  the  comparison  of  the  tests  for  sound- 
ness already  outlined,  a  few  other  tests  which  have  been  sug- 
gested for  use  may  be  briefly  mentioned. 

The  Chloride  of  Calcium  Test  depends  on  the  fact  that  slak- 
ing of  free  lime  is  hastened  by  feeble  solution  of  chloride  of 
calcium.  (See  §  107.)  Concerning  this  test,  Prof.  F.  P.  Spald- 
ing1  says  he  "has  found  it  to  give  true  indications  in  a  number 
of  cases,  including  some  unsound  magnesian  cements.  It  con- 
sists in  mixing  the  mortar  for  the  cakes  with  a  solution  of  40 
grammes  chloride  of  calcium  to  one  liter  of  water,  allowing 
them  to  set,  immersing  them  in  the  same  solution  for  twenty- 
four  hours,  and  then  examining  them  for  checking  and  soften- 
ing as  in  other  tests." 

130.  M.    H.    LeChatelier's    Method.  —  The    method     recom- 
mended by  M.   H.   LeChatelier  for  testing  soundness  requires 
the  use  of  a  cylindrical  mold,  about  l£  inches  in  diameter  and 
of  about  the  same  height,  which  is  made  of  thin  metal  and 


1  "Notes  on  the  Testing  and  Use  of  Hydraulic  Cement,"  by  Fred.  P. 
Spalding. 


82  CEMENT  AND  CONCRETE 

slit  along  a  generatrix.  The'  mortar  is  to  be  placed  in  the 
mold  as  soon  as  made,  and  immersed  at  once  in  cold  water; 
the  mold  is  held  firmly  by  a  clamp,  and  a  flat  plate  at  either 
end  of  the  mold  retains  the  mortar  in  shape  until  set.  When 
setting  has  taken  place,  the  mold  is  undamped  and  the  widen- 
ing of  the  slit  indicates  the  expansion  of  the  mortar.  If  de- 
sired, the  swelling  may  be  increased  and  hastened  by  transfer- 
ring the  mold  and  its  contents  to  hot  water  as  soon  as  the  ce- 
ment is  set.  The  same  writer  has  suggested  a  modification  of 
the  hot  test  by  placing  briquets  in  cold  water  and  gradually 
heating  to  near  the  boiling  point,  this  temperature  being  main- 
tained for  six  hours. 

Various  other  tests  have  been  suggested,  such  as  the  effect 
of  regaging;  withstanding  immersion  as  soon  as  gaged;  allow- 
ing large  thin  cakes  to  harden  in  air  and  striking  them  to  obtain 
a  musical  sound.  Most  of  these  tests,  however,  are  worthy  of 
passing  notice  only. 

131.  Discussion.  —  There  are  but    few  experiments  to  show 
that  a  cement  which  will  actually  fail  and  disintegrate  when 
properly  used,  may  still  pass  the  cold  water  neat  pat  test;  yet 
there  is  no  doubt  that  inferior  cements  may  pass  this  test  per- 
fectly, " inferior  cements"  being  those  which  will  not  give  the 
best  results  in  practice,  though  they  do  not  disintegrate. 

Cement  is  at  present  used  in  a  very  crude  way,  and  it  is  only 
in  exceptional  cases  that  a  poor  quality  of  material  may  be 
detected  in  the  completed  structure.  This  is  sufficient  reason 
why  so  few  failures  can  be  found  in  cement  work  which  may 
be  attributed  to  a  poor  quality  of  cement.  But  in  the  more 
economical  manner  in  which  this  material  is,  even  now,  begin- 
ning to  be  used,  it  is  absolutely  essential  to  know  what  its  fu- 
ture behavior  will  be.  That  the  cement  will  never  be  exposed 
to  hot  water  in  actual  use,  is  a  weak  argument  against  hot 
water  tests.  It  must  be  remembered  that  the  chief  object  of 
testing  cement  is  to  arrange  the  various  products  in  their  true 
order  of  merit,  and  any  system  which  will  effect  this  result  is 
perfectly  legitimate.  On  the  other  hand,  it  is  due  to  the  man- 
ufacturers that  a  test  which  will  occasionally  reject  perfect 
cements  should  not  be  adopted  when  it  is  possible  in  any  other 
way  to  detect  poor  products  with  certainty. 

132.  It  is  possible  that    the  temperature  used  and  recom- 


CONSTANCY  OF  VOLVME  83 

mended  by  Mr.  Faija  is  sufficiently  high  to  detect  unsoundness 
or  a  tendency  to  "blow."  It  has  never  been  clearly  proved 
that  it  is  not,  but  the  higher  temperature  of  70°  to  100°  C.  has 
appeared  to  meet  with  greater  favor.  The  writer  made  a  few 
experiments  to  compare  results  obtained  with  mixtures  of 
Portland  cement  and  lime  when  using  the  temperature  of  110° 
Fahr.  (43°  C.)  with  those  obtained  in  water  at  190°  Fahr.  (88° 
C.),  and  in  water  at  the  ordinary  temperature  of  60°  to  65°  Fahr. 
(16°  to  18°  C.).  Quicklime,  in  proportions  varying  from  one 
to  ten  per  cent.,  was  added  to  the  cement,  and  seven  pats  were 
made  from  each  mixture  of  cement  and  lime. 

These  pats  were  subjected  to  the  following  treatment:  — 

Pat  No.  1,  placed  in  vapor  of  water  at  110°  F.  when  made. 

2,  110°  F.  when  set. 

3,  110°  F.  after  24  hours. 
"        4,                                                     190°  F.  when  made. 

5,  "         190°  F.  when  set. 

6,  "         190°  F.  after  24  hours. 
Above  six  pats  immersed  in  the  hot  water  after  three  hours  in 

vapor. 

Pat  No.  7,  placed  in  cool  water  when  set. 

When  no  lime  was  added,  pats  1,  2  and  3  revealed  no  defects; 
pats  4  and  5  showed  small  cracks  in  two  days,  but  pat  No.  6 
still  adhered  to  the  glass  after  eight  days.  Pat  No.  7  was  perfect 
after  two  months.  With  2  per  cent,  lime  added  to  the  cement, 
pat  No.  1  was  slightly  warped  and  cracked,  and  Nos.  2  and  3 
were  off  glass;  Nos.  4  and  5  were  cracked  and  warped;  No.  6 
was  off  glass,  and  No.  7  became  detached  from  glass  after  two 
months,  but  was  otherwise  perfect.  With  4  per  cent,  lime,  all 
the  pats  failed,  the  one  in  cool  water  being  off  glass,  cracked 
and  warped  after  one  day. 

It  must  be  remembered  that  the  free  lime  occurring  in  cement 
is  of  a  different  character  from  the  quicklime  added  in  these 
tests,  because  the  former  contains  impurities  and  has  been  cal- 
cined at  a  very  high  temperature,  and  would  therefore  slake 
more  slowly.  It  has  been  said  that  as  small  an  amount  as  1 
per  cent  of  free  lime  in  cement  is  dangerous.  If  this  is  true, 
and  it  probably  is,  the  temperature  of  110°  Fahr.  would  seem 
to  be  inadequate  to  quickly  indicate  a  tendency  to  "blow." 


84 


CEMENT  AND  CONCRETE 


133.  Some  of  the  results  obtained  by  M.  Deval  have  already 
been  given  (§  127).  Mr.  Maclay  made  similar  tests  on  several 
samples  of  Portland  cement,  using  a  temperature  of  200°  Fahr., 
but  these  tests  only  permit  of  comparing  the  strength  acquired 
in  cold  water  in  seven  and  twenty-eight  days  with  the  strength 
in  hot  water  at  ages  of  from  two  to  seven  days.  Long  time 
tests,  showing  that  the  cements  which  give  low  results  in  hot 
water  and  normal  results  in  cold  water  on  short  time  tests, 
give  in  reality  a  low  strength  at  the  end  of  six  months  or  more, 
have  been  almost  entirely  lacking  until  very  recently. 

Table  40,  §  226,  gives  some  of  the  results  obtained  by  the 
author  in  hot  tests  and  long  time  cold  tests  on  Portland  cement. 
It  is  seen  that  the  hot  test  at  80°  C.  indicated,  in  seven  days, 

TABLE  26 
Cold  and  Hot  Tests  on  Samples  of  One  Brand  of  Portland  Cement 


CEMENT. 

PARTS. 
SAND 

DATE 
MADE. 
1894. 

AGE. 

TENSILE 
STRENGTH. 

BRIQUETS  STORED. 

Mo.    Pa. 

Moist  air. 

Water. 

B' 

2 

4       1C 

5  da. 

8 

1  da. 

80°  C.     4  da. 

A 

2 

7        2 

5  da. 

235 

1 

4 

B' 

2 

4      10 

7  da. 

13 

1 

6 

A 

2 

7        2 

7  da. 

229 

1 

'          6 

B 

3 

7        2 

7  da. 

197 

1 

15  to  18°  C.    6  da. 

A 

3 

7        2 

7  da. 

108 

1 

6 

B 

3 

7        2 

28  da. 

298 

1 

<     '27 

A 

3 

7        2 

28  da. 

198 

1 

27 

B' 

2 

4      16 

7  mo. 

411 

1 

'          7  mo. 

A 

2 

7        2 

6  mo. 

465 

1 

6    " 

BEHAVIOR  OF  PATS  MADE  JULY  2,  1894 

No.  1  in  vapor,  when  held  \$  wire.  I  Immersed  in  water  80°  C.  after  three 
No.  2  in  vapor,  when  held  1#  wire.  }      hours  in  vapor. 
No.  3  in  tank,  when  held  1#  wire. 
No.  4  in  tank  ;  two  hours  after  held  1#  wire. 

Cement:  A,  No.  1  off  glass  in  two  days;  No.  2  warped  some  in  two  days. 
"        A,  No.  3  O.K.  after  twenty-one  days;  off  glass  and  warped  in 

fifty-two  days. 
"        A,  No.  4  loose  on  glass  in  twenty-one  days;  off  glass  and  warped 

in  fifty-two  days. 

"  B,  No.  1  off  glass  and  warped  some  in  two  days;  No.  2  entirely 
disintegrated  in  two  days;  No.  3  loose  on  glass  in  twenty- 
one  days;  off  glass  and  warped  in  fifty-two  days;  No.  4  loose 
on  glass  in  twenty-one  days ;  off  glass  and  warped  in  fifty-two 
days. 


CONSTANCY  OF   VOLUME  85 

the  inferior  quality  of  sample  W,  although  it  gave  normal  re- 
sults in  cold  water  up  to  twenty-eight  days;  the  two  year  tests 
with  mortars  containing  two  parts  or  more  sand,  show  it  to  be 
inferior.  If  we  attempt  to  carry  the  analogy  too  far,  however, 
we  fall  into  the  error  which  placed  the  hot  test  in  disrepute  for 
several  years,  that  is,  we  must  not  expect  that  the  strength  in 
cold  water  after  a  long  time  will  be  exactly  proportional  to  the 
strength  developed  in  hot  water  in  a  few  days. 

134.  In  Table  26  are  given  the  results  of  tests  by  the  author, 
on  samples  of  a  single    brand  of   Portland  cement.     The  por- 
tion marked  "A"  had  been  spread  out  in  open  air  for  seventy- 
seven   days  in  a  thin  layer.      The   portion   marked   "B"    was 
taken   directly   from   the  barrel  July   2d,   and   B '    was    taken 
from  the  same  barrel  April  16th.     Samples  B  and  B'  are  not 
identical,    because  the    cement   had    undergone    some    change, 
though  stored  in  the  barrel.     Each  result  is  the   mean  of  five 
briquets. 

In  the  short  time  cold  tests  there  was  nothing  to  indicate  that 
the  cement  directly  from  the  barrel  was  not  good,  except  the 
very  small  evidence  in  the  fact  that  pat  No.  3  was  loose  on  glass 
plate  after  twenty-one  days.  In  fact,  the  cold  water  briquet 
tests  at  seven  and  twenty-eight  days  unmistakably  declare  in 
favor  of  the  sample  B.  On  the  other  hand,  how  sharply  did 
the  hot  tests  bring  out  the  defects,  two  days  in  hot  water  being 
sufficient  to  entirely  disintegrate  one  of  the  pats.  Although 
sample  B'  showed  a  considerable  tensile  strength  at  seven 
months  with  two  parts  sand,  yet  the  pats  of  neat  cement  failed, 
even  in  cold  water,  after  two  months,  altogether  too  late  a  date 
to  be  of  any  value  in  preventing  the  use  of  the  cement. 

135.  In  a  paper  read  before  the  American  Society  for  Testing 
Materials,  July,   1903,1  Mr.  W.  P.  Taylor  of  the  City  Testing 
Laboratory,  Philadelphia,  gives  some  very  interesting  data  con- 
cerning the  behavior  of  cements  that  failed  to  pass  the  boiling 
test.     The  method  employed  was  to  make  cakes  of  cement  in 
the  form  of  a  small  egg,  keep  them  in  moist  air  for  twenty-four 
hours,  then  place  them  in  cold  water  which  is  gradually  raised 
to  the  boiling  point  and  maintained  at  that  temperature  for 
three  hours.     The  results  cited  show  that  some  unsound  ce- 


Proceedings  Amer.  Soc.  for  Testing  Materials,  1903. 


86  CEMENT  AND  CONCRETE 

ments  may  be  much  improved  by  sifting  out  the  coarse  parti- 
cles, and  that  a  cement  failing  in  the  boiling  test  when  fresh 
may  pass  it  satisfactorily  after  four  or  five  weeks. 

Examination  of  the  results  showed  that  96  per  cent,  of  a 
large  number  of  specimens  which  did  not  pass  the  hot  water 
test  failed  within  three  hours,  and  99  per  cent,  in  four  hours. 
This  fixes  a  practical  limit  to  the  time  necessary  to  continue 
the  test.  Some  very  valuable  tests  are  cited  to  show  the 
ultimate  failure  in  cold  water  of  samples  that  failed  in  the 
hot  tests.  Ten  cements  which  passed  the  cold  water  pat  test 
of  twenty-eight  days'  duration,  but  which  failed  in  the  boiling 
test  above  described,  gave  normal  results  in  one-to-three  mor- 
tars at  twenty-eight  days,  showing  a  tensile  strength  of  217  to 
252  pounds  per  square  inch,  but  gave  only  47  to  147  Ibs.  per 
square  inch  at  four  months. 

Another  valuable  comparison  is  given  by  Mr.  Taylor:  A 
compilation  of  data,  covering  over  a  thousand  tests  on  many 
varieties  of  cements,  showed  that  "of  those  samples  that  failed 
in  the  boiling  test  but  remained  sound  at  twenty-eight  days  (in 
cold  water),  3  per  cent,  of  the  normal  pats  showed  checking  or 
abnormal  curvature  in  two  months;  7  per  cent,  in  three  months; 
10  per  cent,  in  four  months;  26  per  cent,  in  six  months  and  48 
per  cent,  in  one  year;  and  of  these  same  samples,  37  per  cent, 
showed  a  falling  off  in  tensile  strength  in  two  months;  39  per 
cent,  in  three  months;  52  per  cent,  in  four  months;  63  per  cent, 
in  six  months  and  71  per  cent,  in  one  year." 

136.  It  may  be  of  interest  to  introduce  here  some  of  the 
opinions  that  have  been  expressed  concerning  hot  tests.  M. 
Candlot 1  says  that  cements  of  normal  composition,  the  burning 
of  which  has  not  been  carried  to  the  point  of  vitrification,  would 
be  condemned  by  the  hot  test  of  neat  cement,  although  mor- 
tars made  with  them  show  no  signs  of  alteration  in  sea  water, 
and,  when  preserved  in  air;  give  entirely  satisfactory  results. 
Referring  to  the  tests  of  one-to-three  mortar  briquets  in  water 
at  80°  C.,  he  considers  that  "cements  containing  free  lime  give 
in  hot  water,  lower  resistances  than  in  cold  water;  cements  of 
good  quality  give  resistances  at  least  equal  and  nearly  always 
greater  in  hot  water  than  in  cold.  Cements  well  proportioned 


'Ciments  et  Chaux  Hydrauliques,"  par  M.  Candlot,  pp.  144-145. 


CONSTANCY  OF  VOLUME  87 

and  homogeneous,  but  not  having  obtained  the  maximum  burn- 
ing, give  satisfactory  results  with  this  test." 

In  using  the  slit  cylinders  mentioned  in  §  130,  M.  H.  Le 
Chatelier  found  l  that  the  addition  of  5  per  cent,  of  lime  could 
be  detected  by  cold  tests  in  a  few  hours,  while  5  per  cent,  of 
magnesia  could  not  be  detected  in  twenty-eight  days.  The 
cement  containing  5  per  cent,  lime  disintegrated  almost  at 
once  in  hot  water,  while  the  sample  to  which  5  per  cent,  of  mag- 
nesia had  been  added,  swelled  considerably  in  one  day. 

Mr.  A.  Marichal 2  found  that  "the  percentage  of  water  en- 
tered in  combination,  after  ten  days  in  hot  water,  was  the  same 
as  for  six  months  in  cold  water,  and  that  the  strength  of  the 
cement  was  increasing  with  the  amount  of  water  entered  in 
combination.  It  was  discovered  incidentally,  that  cement  con- 
taining over  5  per  cent,  of  magnesia,  or  3  per  cent,  of  uncom- 
bined  lime,  would  not  stand  the  boiling  test." 

137.  Hot    Tests   for    Natural   Cements.  —  All  that  has  pre- 
ceded concerning  hot  tests  refers  to  their  use  for  testing  Port- 
land cements.     Very  little  is  known  concerning  the  value  of  hot 
tests  for  natural  cements.     There  are  comparatively  few  natural 
cements  that  are  absolutely  bad,  but  to  distinguish  between  the 
first  and  second  quality  of  this  variety  of  products  is  much  more 
difficult  than  to  make  a  similar  distinction  with  Portlands.     One 
point  is  certain,  natural  cements  must  not  be  expected  to  with- 
stand boiling  water.     Mr.  de  Smedt  experimented  with  fifteen 
brands  of   natural   cement,   and  found   that  thirteen  of  them 
went  to  pieces  in  boiling  water  in  two  hours,  although  none  of 
them  was   thought  to   contain    caustic  lime.       Prof.   Tetmajer 
has  stated  that  for  Roman  cements,  boiling  water,  or  even  75°  C., 
is  not  at  all  conclusive,  and  recommends  50°  C.  for  trial,  but  our 
natural  cements  are  not  strictly  comparable  with  Roman  ce- 
ments. 

138.  The  author  has  experimented  with  three  temperatures, 
namely,  50°,  60°,  and  80°  C.,  and  is  inclined  to  consider  that 
80°  C.  is  likely  to  give  the   most   useful   information  for  sand 
mortar  briquets    but    not   for   neat  cement   pastes.     Table  41, 
§  227,  gives  the  results  of  hot  briquet   tests  on  six  brands  of 


"  Tests  Hydr.  Materials,"  by  H.  LeChatelier. 
8  Trans.  Amer.  Soc.  C.  E.,  Vol.  xxvii,  p.  438. 


88  CEMENT  AND  CONCRETE 

natural  cement.  It  is  seen  that,  with  two  parts  sand,  brands 
Jn,  Hn,  and  Bn,  give  very  low  results  at  80°  C.',  and  these  brands 
are  really  inferior  cements  as  shown  by  the  two-year  cold  tests. 
Brand  Jn  is  the  only  one  that  gave  a  lower  result  at  seven  days 
than  at  five  days  when  tested  at  80°  C.,  and  this  brand  failed 
entirely  at  two  years,  though  it  gives  normal  results  in  cold 
water  up  to  six  months.  Neat  cement  pats  of  this  brand,  after 
being  stored  in  cold  water  for  nearly  one  year,  were  found  to  be 
cracked,  although  they  had  been  perfect  after  one  month  in 
cold  water.  It  was  also  found  that  neat  cement  pats  of  this 
brand  warped  and  cracked  in  two  days  when  placed  in  water  of 
60°  C.  when  set. 

139.  CONCLUSIONS.  ~  It  may  be  said  that  although  the 
limits  within  which  the  hot  tests  are  reliable  have  not  been  well 
established,  and  although  a  strict  adherence  to  them  may  at 
times  reject  a  usable  product,  yet  it  is  believed  that  sufficient 
experiments  have  been  made  to  indicate  that  they  are  of  much 
value,  and  should  be  made  in  all  cases  where  the  quality  of  the 
cement  is  of  high  importance. 

The  present  indications  seem  to  be  that  Portland  cements 
may  well  be  tested  in  the  form  of  neat  cement  pats  and  sand 
mortar  briquets  at  a  temperature  of  about  80°  C.  Natural  ce- 
ments in  the  form  of  neat  paste  should  not  be  called  upon  to 
resist  a  temperature  above  60°  C.,  but  80°  C.  will  probably  give 
the  most  useful  information  with  sand  mortars.  In  either  case, 
the  mortar  should  be  allowed  to  set  in  moist  air  of  ordinary 
temperature,  then  transferred  to  the  vapor,  to  remain  two  or 
three  hours  before  immersion  in  the  hot  water.  It  is  not  rec- 
ommended that  these  hot  tests  should  replace  the  ordinary 
cold  tests,  but  simply  that  in  cases  where  the  extra  work  in- 
volved is  not  prohibitive,  the  hot  tests  should  be  made  in  con- 
nection with  the  cold  tests. 


CHAPTER  VIII 

TESTS   OF  THE  STRENGTH  OF  CEMENT  IN  COMPRES- 
SION,   ADHESION,   ETC. 

140.  IN  testing  the  strength  of   cement  the  object  is  three- 
fold :    1st,  to  obtain  an  idea  of   the  strength  that  may  be  ex- 
pected from  the  cement  as  used  in  the  structure;  2d,  to  obtain  a 
basis  for  comparing  the  value  of  different  cements  in  this  regard; 
and  3d,  to  determine  the  ability  of  the  cement  to  withstand 
destructive  agencies,  whether  these  agencies  be  due  to  exterior 
causes  or  emanate  from  the  character  of  the  cement  itself.     To 
illustrate  the  last  point  it  is  only  necessary  to  mention  such  de- 
stroying agents  as  free  lime  (interior)  and  frost  (exterior).     It  is 
evident  that  the  stronger  the  cement  the  more  effectually  will 
these  agencies  be  resisted. 

The  strength  of  cement  may  be  tested  by  compression, 
shearing,  bending,  adhesion,  abrasion  and  tension.  The  tensile 
test  is  the  one  most  frequently  used,  but  the  tests  will  be  con- 
sidered in  the  order  named. 

ART.  19.    TESTS  IN  COMPRESSION  AND  SHEARING 

141.  Value  of  Test.  —  In   practically  all  forms  of   masonry 
construction,  cement  is  called  upon  to  resist  compression.     In 
consequence  of  this  fact,  the  opinion  is  somewhat  general  that 
the  greatest  amount  of  information  would  be  obtained  by  com- 
pressive  tests.     But  the  compressive  strength  of  cement  is  so 
much  greater  than  its  tensile  strength,  that  when  failures  occur, 
they  are  likely  to  be  due  to  other  forms  of  stress.     In  short,  the 
ratio  of  the  compressive  strength  to   the   crushing  force  it  is 
likely  to  be  called  upon  to  resist,  is  usually  much  greater  than 
the  corresponding  ratio  in  tensile  strength. 

142.  There  is  no  doubt  that  compressive  tests  are  of  much 
interest  and  value,  especially  so  since  the  use  of  concrete  and 
steel  in  combination  has  become  general,  but  as  yet  the  facili- 
ties for  making  the  test  are  not  available  without  considerable 
expense.     This  is  on  account  of  the  larger  force  required  (the 

89 


90  CEMENT  AND  CONCRETE 

compressive  strength  being  six  to  ten  times  the  tensile)  and  be- 
cause the  uniform  distribution  of  the  stress  over  the  surface  of 
the  specimen,  and  the  accurate  recording  of  the  force  exerted, 
are  even  more  difficult  than  the  corresponding  operations  in 
tensile  tests.  Prof.  Sondericker,1  in  a  paper  read  before  the 
Boston  Society  of  Civil  Engineers,  describes  an  apparatus  in 
which  he  seems  to  have  overcome  a  part  of  these  difficulties. 

A  convenient  specimen  for  compressive  tests  is  a  cube  meas- 
uring two  inches  on  a  side.  The  specimens  are  prepared  and 
treated  in  the  same  way  as  briquets  for  tensile  tests.  Before 
testing,  two  opposite  faces  of  the  cubes  are  usually  ground  so  as 
to  be  true  planes,  parallel  to  each  other,  or  the  opposite  sides 
may  be  faced  with  plaster  of  Paris,  though  this  is  not  recom- 
mended. Grinding  two  surfaces  to  true  planes  increases  very 
much  the  work  involved  in  testing,  so  that  several  tensile  tests 
may  be  made  in  the  time  required  to  make  one  compressive  test. 
143.  Conclusions.  —  Although  tests  of  compressive  strength 
are  of  interest  from  a  scientific  point  of  view,  it  is  not  considered 
that  they  would  give  much  greater  information  concerning  the 
relative  qualities  of  cements  than  is  given  by  tensile  tests,  and 
therefore  they  need  not  be  included  in  an  ordinary  series  of 
acceptance  tests. 

144.  Tests  of  Shearing  Strength.  —  Although  cement  is  fre- 
quently called  upon  to  withstand  a  shearing  stress,  tests  of  this 
kind  are  very  seldom  made.  Some  of  the  difficulties  encoun- 
tered in  compressive  tests  are  also  present  in  tests  of  shearing. 
Prof.  Cecil  B.  Smith  made  quite  an  extended  series  of  shearing 
tests  by  cementing  together  three  bricks,  the  middle  one  pro- 
jecting above  the  other  two,  and  the  pressure  being  so  applied 
as  to  avoid  any  transverse  stress.  It  is  evident  that  by  this 
method  the  adhesive  strength  is  also  brought  into  play.  Shear- 
ing tests  need  not  be  included  in  normal  tests  of  quality. 

ART.  20.    TESTS  OF  TRANSVERSE  STRENGTH 

145.  It  is  probable  that  the  earliest  rupture  tests  of  cement 
were  made  by  submitting  rectangular  prisms  to  a  bending 
stress;  but  such  tests  have  long  held  a  place  subordinate  to 
trials  of  tensile  strength.  A  mass  of  masonry,  taken  as  a  whole, 
is  very  apt  to  be  subjected  to  a  bending  stress,  but  it  is  a  ques- 


Jour.  Assoc.  Engr.  Soc.,  Vol.  vii,  p.  212. 


TRANSVERSE    TESTS  91 

tion  whether  a  transverse  test  on  a  small  specimen  gives  any 
better  idea  of  the  ability  of  a  large  beam  to  carry  its  load,  than 
do  simple  tensile  and  compressive  tests. 

In  Engineering  News  of  December  14,  1893,  appeared  an 
article  giving  the  comparative  results  obtained  in  tensile  and 
transverse  tests.  The  tensile  specimens  had  an  area  of  one 
square  inch  at  the  smallest  place,  and  the  transverse  specimens 
also  had  an  area  of  cross-section  of  one  square  inch.  It  was 
found  that  the  modulus  of  rupture  computed  by  the  common 

3  W I 
formula/  =    .   . 2  was  from  1.1  to  3.8  times  the  tensile  strength 

developed  by  the  briquets.  Some  comparative  tests  made  at 
St.  Mary's  Falls  Canal  are  discussed  in  Art.  56. 

146.  The  objections  to  transverse  tests  are:  1st,  if  the  speci- 
mens are  made  but  one  inch  in  cross-section,  it  is  difficult  to 
handle  them  without  injuring  them,  and  if  the  section  is  made 
much  larger  than  one  inch  square,  a  much  greater  amount  of 
cement  is  required  to  make  the  specimens    and  more  room  re- 
quired to  store  them;  2d,  it   would  seem    that  the  results  ob- 
tained might  be  less  trustworthy  than  those  in  tensile  tests 
because  of  the  greater  influence  of  the  outside  layers,  which  are 
subjected  to  the  greatest  accidental  variations,  on  the  apparent 
strength  of  the  specimen.     On  the  other  hand,  it  may  be  said 
that,  when  no  testing  machine  is  at  hand,  the  apparatus  requi- 
site to  make  a  crude  test  may  easily  be  improvised.     All  that  is 
required  is  a  rectangular  wooden  mold,  three  knife  edges,  and  a 
pail  with  a  quantity  of  sand  or  water. 

147.  When  it   is  a  question  of  making  tests  of  transverse 
strength  accurately  and  rapidly,  the  apparatus  required  is  no 
more  simple  than  the  apparatus  for  tensile  tests.     In  the  con- 
struction of  metal  molds  in  large  quantities  it  makes  little  dif- 
ference whether  the  form  requires  curved  or  straight  lines.     As 
far  as  breaking  is  concerned,  there  is  a  certain  force  to  be  applied, 
and  a  machine  that  will  answer  for  one  test  may  also  be  used 
for  the  other.     In  the  matter  of  clips,  there  may  be  a  slight 
advantage  as  to  simplicity  in  a  clip  designed  for  transverse 
breaking. 

In  making  transverse  tests  the  author  has  used  a  form  two 
inches  square  and  eight  inches  long.  By  placing  the  end  sup- 
ports five  and  one-third  inches  apart,  the  modulus  of  rupture 


92  CEMENT  AND  CONCRETE 

by  the  formula  /  =    ,  ,2  becomes  equal  to  W,  the  center  load 

applied. 

148.  Finally,  it  may  be  said  that  there  is  little  objection  to 
substituting  transverse  tests  for  tensile  tests,  although  no  evi- 
dent  advantage   would   be   gained.     It   would   also   seem   that 
there  is  no  object  in  making  tests  for  quality  by  both  trans- 
verse  and   tensile   tests,    though   from   a   scientific   standpoint 
comparative  tests  of  transverse  and  tensile  strength  are  of  great 
interest. 

ART.  21.   TESTS  OF  ADHESION  AND  ABRASION 

149.  ADHESION. — The  test  for  adhesion  is   also  one  of  long 
standing,  being  used  during  that  time  when  engineers  were  con- 
tent with  an  approximate  idea  of  what  might  be  expected  of  an 
hydraulic  product.     It  has  been  stated  above  that  when  failure 
occurs  in  a  mass  of  masonry,  it  is  more  frequently  a  failure  in 
tension  than  in  compression;  it  may  be  added,  that  it  is  also 
more  likely  to  fail  in  adhesion  than  in  cohesion.     Hence,  an 
adhesive  test  is  a  very  proper  one  to  make,  and  will  give  most 
valuable  results.     In  fact,  it  is  perhaps  the  most  rational  rup- 
ture test,  and  were  it  not  for  the  difficulties  involved  in  its  ap- 
plication, it  would  doubtless  come  into  general  use. 

150.  One  of  the  greatest  difficulties  experienced  in  making 
adhesive  tests  is  the  preparation  of  the  specimens  of  stone  or 
other  material  to  which  the  mortar  is  to  adhere.     In  early  ex- 
periments common  brick  were  used,  or  pieces  of  stone  were  cut 
to  the  same  shape  as  brick,  and  two  or  more  pieces  cemented 
together.     In  later  methods  the  flat  surfaces  of  two  specimens 
are  sometimes  joined  with  their  axes  at  right  angles,  thus  mak- 
ing the  cemented  surface  square.     The  upper  brick  being  held 
on  two  supports,  a  load  is  applied  to  the  lower  brick. 

151.  Mr.  I.  J.  Mann,  in  a  paper  presented  to  the  Institution 
of  Civil  Engineers,1  described  a  method  of  testing  adhesion  in 
which  are  used  test  pieces  1^  inches  long  by  1  inch  wide  by  J  to 
|  inch  thick.     These  are  cemented  together  in  a  cruciform  shape, 
and  a  simple  spring  balance  machine  with  properly  arranged 
levers  pulls  them  apart.     The  upper  block  is  supported  at  its 
ends  and  an  inverted  U-shaped  piece  bears  upon  the  ends  of 


Proc.  Inst.  C.  E.,  Vol.  Ixxi,  p.  251. 


TRANSVERSE   TESTS  93 

the  lower  block.  The  stress  is  applied  through  a  conical  shaped 
pivot  bearing  on  the  U-shaped  saddle.  Mr.  Mann  states  that 
test  pieces  may  be  made  either  of  plate  glass  or  close  grained 
limestone,  the  latter  being  sawn  into  pieces  of  the  right  size. 

152.  Another  method    is  to  make  test  pieces  to  fit  one  end 
of  the  mold  used  for  tensile  tests,  and  after  placing  the  piece  of 
stone  in  the  mold,  to  fill  the  other  end  with  the  mortar  to  be 
tested.     The  objection  to  this  method  is  the  expense  of  pre- 
paring pieces  of  this  form.     It  has  been  suggested  to  substitute 
artificial  stone  for  the  cut  stone  samples.     Thus,  suppose  it  is 
required  to  test  the  adhesion  of  a  certain   mortar  to  granite: 
mold  half  briquets  of  a  mixture  of  ground  granite  with  cement, 
and  after  these  have  well  hardened,  replace  them  in  the  mold 
and  fill  the  other  end  of  the  mold  with  the  mortar  to  be  used. 
It  is  quite  certain  that  the  same  result  would  not  be  obtained 
in  this  way  as  though  the  specimens  were  cut  from  a  piece  of 
solid  granite. 

153.  One  of    the  simplest  methods  of  applying  this  test  is 
one  which  the  author  has  used  for  some  time.     The  test  pieces 
are  in  the  form  of  flat  plates  one  inch  square  and  one-fourth 
inch  or  less  in   thickness.     These  plates  being  placed  in   the 
center  of  a  briquet  mold,  the  ends  of  the  mold  are  filled  with 
mortar.     The    plates    may    be    improved    by    cutting    shallow 
grooves  in  two  opposite  sides  to  make  a  more  perfect  fit  with 
the  sides  of  the  mold.     This  may  easily  be  done  with  a  round 
file.     Besides  the  simple  form  of  the  test  pieces  and  consequent 
ease  of  making  them,  this  method  has  the  further  advantage 
that  a  test  may  be  made  almost  as  readily  and  accurately  as  a 
tensile  test  of  cohesion.     Also,  since  the  adhesive  area  is  one 
square  inch,  the  results  may  be  compared  with  cohesive  tests 
on  specimens  having  the  same  area  of  cross-section. 

154.  The    experiments  on  adhesive  strength   made  by   Mr. 
Mann  were  probably  more  extensive  than  any  others  published. 
His  results  are  useful  mainly  as  showing  the  lack  of  cementitious 
properties  in  the  coarser  grains  of  cement,  and  this  point  he 
proves  very  clearly  by  quite  a  large  number  of  experiments. 
It  was  also  developed  that  cement  that  had  been  rendered  slow 
setting  by  aeration  or  " cooling"  gave  a  lower  adhesive  strength 
than  samples  directly  from  the  makers,  which  set  more  rapidly. 
But  the  method  followed  by  Mr.  Mann,  of  immersing  the  speci- 


94  CEMENT  AND  CONCRETE 

mens  as  soon  as  cemented  together,  may  have  had  something  to 
do  with  this  result;  the  quicker  setting  samples  would  earlier 
resist  the  injurious  action  which  is  likely  to  follow  the  immer- 
sion of  such  small  quantities  of  mortar  before  they  have  set. 

155.  All  of  the  things  which  influence  the  results   in  testing 
the  cohesive  strength  must  also  be  considered  as  affecting  the 
adhesive  test.       The  consistency  of  the  mortar,  the  method  of 
gaging,  the  pressure  applied  in  cementing  the  specimens,  and 
the  conditions  of  storage  until  the  time  of  breaking,   will  all 
have  an  influence  on  the  result  obtained.     In  addition  to  these, 
the  character  of  the  samples  as  to  the  kind  of  stone  used,  its 
structure,  the  physical  condition  of  the  surfaces,  etc.,  must  all 
be  considered.     It  is  therefore  clear  that  many  difficulties  must 
be  met  before  the  test  for  adhesion  can  ever  be  included  in 
standard  tests. 

156.  Special  tests  directed  toward  ascertaining  the  compara- 
tive adhesion  of  cement  to  different  varieties  of  stone,  the  effect 
of  the  various  differences  in  manipulation,  the  comparative  ad- 
hesion of  mortars  containing  various  proportions  of  sand,  etc., 
are  of  undoubted  value.     But,  before  the  adhesive  test  can  be 
considered  a  normal  one  for  cement,  much  of  this  experimental 
work  will  be  required. 

The  results  of  a  number  of  adhesive  tests  made  under  the 
author's  direction  are  given  in  Art.  51. 

157.  TESTS  OF  ABRASION.  —  Abrasion  tests  of   cement   are 
not  at  all  common,  and  for  the  ordinary  uses  to  which  cement 
is  put,  its  resistance  to  such  action  is  of  little  interest  except  as 
it  may  imply  other  kinds  of  strength.     Occasionally,  however, 
it  may  be  desired  to  have  a  mortar  which  will  withstand  wear, 
as,  for  instance,  in  making  concrete  walk.     In  such  cases,  tests 
for  resistance  to  abrasion  have  some  interest  and  value. 

The  test  is  usually  made  on  a  sample  prepared  as  for  tensile 
or  compressive  tests,  by  submitting  it  to  the  wearing  action  of 
an  emery  or  grindstone,  or  a  cast  iron  disc  covered  with  sand. 
The  number  of  revolutions  of  the  stone  or  disc  is  recorded, 
automatically  if  possible,  and  the  loss  of  weight  is  determined 
after  a  given  number  of  revolutions. 

A  few  tests  of  this  kind  made  at  St.  Mary's  Falls  Canal  are 
given  in  Art.  58. 


CHAPTER  IX 

TENSILE  TESTS   OF   COHESION 

158.  THE  testing  of  cement  by  applying  tensile  stress  to  a 
previously  prepared  briquet,  containing  definite  proportions  of 
cement  and  water,  or  of  cement,  sand  and  water,  is  the  strength 
test  which  is  now  in  most  general  use.     The  value  of  this  method 
in  comparison  with  that  of  other  forms  of  rupture  tests  has  al- 
ready been  briefly  discussed. 

That  cement  fails  oftener  in  tension  than  in  compression  is 
one  reason  for  preferring  the  tensile  test.  Its  ready  applica- 
bility is  a  still  more  important  point  in  its  favor. 

ART.  22.   SAND  FOR  TESTS 

159.  Whether  the  tensile  test  should  be  applied    to  neat  ce- 
ment briquets  or  to  those  prepared  from  sand  mortars  has  been 
a  disputed  point,  but  there  are  now  but  few  authorities  who 
recommend  the  use  of  the  neat  test  exclusively.     When  tests 
for  soundness  are  not  carefully  made,  the  behavior  of  the  cement 
in  neat  briquets  gives,  perhaps,  a  better  idea  as  to  the  reliability 
of  the  cement  than  do  sand  tests,  but  otherwise  the  sand  test  is 
a  better  index  of  the  value  of  the  cement.     The  principal  ob- 
jection to  the  sand  test  is  that  the  use  of  sand  introduces  another 
cause  of  variation  in  the  results  obtained  by  different  experi- 
menters.    This  objection  has  considerable  weight,  because  it  is 
impracticable  to  find  sand  in  widely  separated  localities  which 
is  absolutely  the  same  in  composition  and  physical  properties; 
but  two  cements  which  appear  to  be  of  equal  value  when  tested 
neat  may  exhibit  quite  different  characteristics  when  used  with 
sand,  and  it  is  believed  that  this  fact  far  outweighs  the  objec- 
tion noted.     As  soon  as  regularity  in  sieves  is  established,  the 
size  of  the  sand  grains  may  be  regulated.     The  chemical  and 
physical  properties  of  the  sand  and  the  shape  of  the  grains  is  a 
more  difficult  matter.      The  crushed  quartz  that  is  used  in  the 
manufacture  of  sandpaper  was  recommended  by  the  Committee 

95 


96 


CEMENT  AND  CONCRETE 


of  the  American  Society  of  Civil  Engineers  of  1885,  and  if  some 
care  is  taken  to  select  that  which  is  clean  and  made  from  pure 
quartz,  there  is  little  difficulty  in  obtaining  a  uniform  product 
of  this  kind. 

160.  The  German  Normal  Sand  is  obtained  by  washing  and 
drying  a  natural  quartz  sand.  In  various  parts  of  Germany 
sand  answering  the  purpose  may  be  found.  Some  tests  made 
in  this  country  to  compare  the  " normal"  German  sand  with 
American  crushed  quartz  have  shown  the  sand  to  give  a  some- 
what higher  strength,  while  other  tests  have  shown  an  opposite 
result.1  A  few  of  these  tests  are  given  in  Table  27. 


TABLE    27 

Results  Obtained  -with  German  "Normal"  and  American 
ard"  Sand  in  Three  Laboratories 


Stand- 


SAND. 

AGE. 
Days. 

STRENGTH  OF  MORTAR, 
1  CEMENT,  3  SAND,  OBTAINED  AT 
LABORATORY  NUMBER 

3 

4 

5 

Normal           

7 
7 
28 
28 

218 
253 
317 
334 

173 
219 
341 
300 

201 
211 
281 
283 

Standard   

Normal      

Standard    

PER  CENT.  OF  WATER  USED. 

8 
9 

9 
10 

.  .  . 

Standard   

Mr.  Max  Gary  has  stated  that  "the  Russian  standard  sand 
gives  markedly  lower,  and  the  Swiss  sand  considerably  higher, 
strength  than  the  German." 

161.  Tests  with  Natural  Sand.  —  It  is  not  to  be  concluded 
from  what  has  preceded  that  one  must  make  mortar  tests  with 
a  "standard"  sand  only.  On  the  contrary,  one  may  obtain 
valuable  results  by  using  in  tests  the  sand  which  it  is  proposed 
to  use  on  the  work.  The  only  point  to  be  insisted  upon  is  that 
a  cement  shall  not  be  rejected  on  account  of  the  poor  quality 
of  the  sand  used  in  testing.  It  is  thus  very  desirable  that  a 
certain  proportion  of  the  tests  be  made  with  a  pure  quartz 
sand,  and  by  making  parallel  tests  with  the  natural  sands,  the 


Article  by  Clifford  Richardson,  Engineering  Record,  Aug.  4,  1894. 


MAKING  BRIQUETS  97 

coefficient  of  the  latter  may  be  obtained.  In  any  case  it  is 
necessary,  in  order  to  obtain  comparable  results,  to  sift  the 
sand  used  for  tests. 

162.  Fineness  of  Sand  for  Tests.  —  The  American  practice  in 
using  crushed  quartz  is  to  reject  the  coarser  particles  by  a  sieve 
having  20  meshes  per  linear  inch  (holes  about  .03  inch  square) 
and  to  reject  the  finer  particles  by  a  sieve  of  30  meshes  per  linear 
inch  (holes  about  .02  inch  square).     The  size  of  grain  of  German 
normal  sand  is  practically  the  same.     In  using  a  natural  sand 
it  is  not  necessary  to  use  this  size  of  grain,  but  it  is  better  to  do 
so,  or  at  least  to  use  some  definite  size  or  definite  combination 
of  sizes;  as,  for  instance,  one-half  of  20  to  30  (passing  holes  .03 
inch  square  and  not  passing  holes  .02  inch  square)  and  one-half 
30  to  50  (passing  holes  .02  inch  square  and  failing  to  pass  holes 
.012  inch  square).     Such  a  method  will  permit  of  duplicating  a 
given  size  of  grain  at  any  time,  while  if  the  sand  is  used  as  it 
occurs  in  nature,  considerable  variations  will  be  found.     The 
effect  of  the  quality  of  sand  on  the  strength  obtained  is  dis- 
cussed in  Chapter  XL 

ART.  23.    MAKING  BRIQUETS 

163.  Proportions.  —  The  proportions  of  the  ingredients  should 
always  be  determined  by  weight  rather  than  by  measure.     It 
will  be  found  more  convenient  to  use   metric  weights  for  the 
dry  ingredients.     The  water  should  then  be  measured  in  cubic 
centimeters,  which  is  equivalent  to  weighing  it  in  grams.     The 
proportion  of  sand  to  be  used  for  mortar  briquets  will  depend 
upon  circumstances,  but  for  short  time  (seven  day)  tests  good 
results  are  not  usually  obtained  with  natural  cement  if  more 
than  two  parts  of  sand  by  weight  are  added  to  one  part  of  ce- 
ment.    Portland   cement  may  be   tested   at  seven  days  with 
three  parts  of  sand  to  one  of  cement.     If  too  large  a  proportion 
of  sand  is  used,  the  briquets  are  liable  to  be  injured  in  handling, 
and  very  low  strengths  are  not  as  accurately  recorded  by  the 
testing  machine. 

164.  CONSISTENCY:    DETERMINATION.  —  The   consistency  of 
the  mortar  has  such  a  marked  influence  on  the  strength  obtained 
that  its  importance  can  hardly  be  overestimated.     The  difficul- 
ties attendant  upon  specifying  the  consistency  of  a  given  mortar 
have  already  been  touched  upon  in  §  116.      The  Committee  of 


98  CEMENT  AND  CONCRETE 

the  American  Society  of  Civil  Engineers  of  1885  recommended 
the  use  of  a  " stiff  plastic"  mortar,  but  this  phrase  has  had  va- 
rious interpretations. 

The  present  Committee  in  its  progress  report l  recommended 
the  use  of  the  Vicat  apparatus:  "In  making  the  determination, 
500  gr.  (17.64  oz.)  of  cement  are  kneaded  into  a  paste,  and 
quickly  formed  into  a  ball  with  the  hands,  completing  the  oper- 
ation by  tossing  it  six  times  from  one  hand  to  the  other,  main- 
tained six  inches  apart;  the  ball  is  then  pressed  into  the  rubber 
ring  (§  98)  through  the  larger  opening,  smoothed  off,  and  placed 
(on  its  large  end)  on  a  glass  plate,  and  the  smaller  end  smoothed 
off  with  a  trowel;  the  paste,  confined  in  the  ring  resting  on  the 
plate,  is  placed  under  the  rod  bearing  the  cylinder,  which  is 
brought  in  contact  with  the  surface  and  quickly  released.  The 
paste  is  of  normal  consistency  when  the  cylinder  (1  cm.  in  di- 
ameter and  loaded  to  weigh  300  grams)  penetrates  to  a  point  in 
the  mass  10  mm.  (0.39  in.)  below  the  top  of  the  ring.  Great 
care  must  be  taken  to  fill  the  ring  exactly  to  the  top." 

The  following  simple  test  taken  from  French  specifications 
will  determine  a  good  consistency  of  mortar  to  'use  for  briquets. 
It  should  be  capable  of  being  easily  molded  into  a  ball  in  the 
hands,  and  when  dropped  from  a  height  of  one  and  a  half  feet 
on  a  hard  slab,  this  ball  should  retain  its  rounded  form  without 
cracking.  The  mortar  should  also  leave  the  trowel  clean  when 
allowed  to  drop  from  it.  Were  a  smaller  quantity  of  water 
used,  the  mortar  would  be  crumbly  and  the  ball  would  crack 
when  dropped  on  the  slab,  while  a  larger  amount  of  water  would 
cause  the  mortar  to  adhere  to  the  trowel  and  the  ball  would  be 
flattened  by  striking  the  slab. 

165.  Another  method  of  determining  the  proper  consistency, 
which  the  author  believes  will  prove  very  satisfactory,  is  to 
make  several  batches  of  mortar  containing  the  same  weights  of 
cement  and  sand,  but  having  different  percentages  of  water. 
As  each  batch  is  mixed,  the  volume  of  the  resulting  mortar  is 
measured  by  pressing  it  lightly  into  a  metal  cylinder  (a  small 
tin  pail  will  answer  the  purpose),  taking  pains  to  fill  the  cylinder 
in  the  same  manner  each  time.  That  batch  of  mortar  which 


1  Proc.  Amer.  Soc.  C.  E.,  Jan.  1903;   also  Engineering   News,  Jan.  29, 
1903,  and  Engineering  Record,  Jan.  31,  1903. 


CONSISTENCY  OF  MORTAR 


99 


occupies  the  least  volume,  when  thus  lightly  packed,  is  the  one 
in  which  the  amount  of  water  used  is  most  nearly  correct. 
Should  either  the  mortar  which  contained  the  least  water  or 
that  which  contained  the  most  water  chance  to  have  the  least 
measured  volume,  then  more  trials  must  be  made  until  such  a 
consistency  is  obtained  that  either  more  or  less  water  will  in- 
crease the  bulk  of  the  mortar.  This  method  will  give  a  con- 
sistency somewhat  more  moist  than  that  which  gives  the  highest 
results  on  short  time  cohesive  tests,  but  it  is  believed  that  where 
briquets  are  made  by  hand,  more  uniform  results  will  be  ob- 
tained when  the  mortar  is  a  trifle  moist.  This  method  is  not 
suited  to  daily  use,  as  it  requires  too  much  time,  but  is  valuable 
as  a  check  on  one's  ideas  of  proper  consistency. 

166.  EFFECT  OF  CONSISTENCY  ON   TENSILE   STRENGTH.— 
Tables  28  and  29  give  a  few  of  the  results  obtained  by  the  author 

TABLE   28 

Variations  in  Consistency  of  Mortar. — Effect  oil  Tensile  Strength, 
Neat  Natural  Cement 


TENSILE  STRENGTH,  POUNDS  PER  SQUARE  I.\<-H. 

CKMKNT. 

WATER  USED  Kx  PRESSED  AS 

AGE  OF 

PER  CENT.  OF  DRY  JNUKEDIENTS  MY  WEHJHT. 

BRIQUKTB. 

Brand. 

Sample. 

25% 

30% 

3T>% 

40% 

4f,% 

Gil 

83  R 

7  days 

1136 

205d 

122/ 

7*0 

6U 

Gil 

84  R 

926 

7'2d 

f>8/ 

540 

39A 

All 

G 

162c 

165e 

108/ 

log 

54A 

An 

N 

1526 

194c 

204e 

134/ 

7% 

Hn 

26  S 

226d 

176/ 

900 

56A 

35i 

Gn 

83  R 

28  days 

181)6 

244d 

211/ 

1820 

136ft 

Gn 

84  R 

1406 

168<I 

114/ 

107(7 

108/i 

An 

G 

210c 

228e 

165/ 

1020 

80A 

An 

N 

1736 

28(5c 

254e 

208/ 

150^ 

Hn 

26  S 

333d 

309/ 

2170 

121A 

89i 

Ln 

31  S 

1  day 

162c 

148e 

97/ 

630 

S6A 

Ln 

u 

7  days 

178c 

177e 

124/ 

710 

45/t 

Ln 

it 

28  days 

207c 

257e 

202/ 

1400 

88A 

Ln 

n 

3  mos. 

SOOc 

389e 

888/ 

2('Ag 

197/1 

SIGNIFICANCE  OF  LETTERS 

a  —  barely  damp. 

6  —  very  dry ;  no  moisture  shown  on  surface  briquets. 

c  —  dry ;  slight  moisture  shown  on  surface  briquets. 

d  —  trifle  dry. 

e  —  about  right  consistency. 

/  — trifle  moist. 

g  —  moist. 

h  —  very  moist ;  would  just  hold  shape. 

i  —extremely  moist;  would  not  hold  shape. 


100  CEMENT  AND  CONCRETE 

in  tests  to  determine  the  effect  of  consistency  on  the  tensile 
strength  of  natural  cement  mortars.  All  of  the  briquets  were 
made  in  the  usual  manner  and  stored  in  fresh  water  until  time 
of  breaking..  Each  result  given  is  the  mean  of  from  two  to  ten 
briquets.  The  letters  affixed  to  each  result  indicate  the  degree 
of  moisture  which  the  mortar  appeared  to  have  when  mixed, 
varying  from  "a,"  barely  damp,  to  "i,"  so  wet  that  the  mortar 
could  not  hold  its  shape  when  laid  on  a  glass  slab. 

The  results  in  Table  28  were  obtained  with  neat  cement  mor- 
tars of  several  brands  of  natural  cement.  The  first  point  to  be 
noted  is  the  variation  in  the  amount  of  water  required  by  dif- 
ferent samples  to  give  the  same  consistency;  thus,  Brand  An, 
sample  N,  when  mixed  with  35  per  cent,  water,  appeared  to 
have  about  the  same  consistency  as  did  sample  G  of  the  same 
brand  mixed  with  30  per  cent.  It  is  also  apparent  that  the 
strength  of  all  samples  is  not  affected  alike  by  given  variations 
in  the  amount  of  water  used  in  mixing;  comparing  the  results 
obtained  when  45  per  cent,  water  is  used  with  that  given  when 
25  per  cent,  water  is  used,  it  is  seen  that  at  seven  days  the  wet 
mortar  gives  42  per  cent,  of  the  strength  obtained  with  dry  mor- 
tar for  sample  84  R,  Brand  Gn,  while  with  the  sample  of  Brand 
Hn  the  strength  of  the  wet  mortar  briquet  is  but  16  per  cent. 
of  that  given  by  the  dry  mortar.  Of  the  six  samples  tested  at 
seven  days  and  twenty-eight  days,  three  gave  the  highest 
strength  at  seven  days  when  mixed  with  25  per  cent,  water, 
and  five  gave  the  highest  strength  at  twenty-eight  days  when 
30  per  cent,  water  was  used.  The  results  on  Brand  Ln  show 
the  greater  proportionate  gain  with  age  of  the  wet  briquets. 

Table  29  shows  similar  results  for  mortars  made  with  one, 
two  and  three  parts  sand.  With  one  part  sand  the  wet  mortar 
made  from  Gn,  21  R,  which  gave  but  22  pounds  per  square 
inch  at  seven  days,  gave  429  pounds,  or  nearly  the  highest 
strength,  at  six  months.  A  similar  result  is  shown  for  sample 
15  R  of  the  same  brand  when  mixed  with  two  parts  sand,  the 
highest  strength  at  one  year  and  two  years  being  given  by  the 
mortar  containing  the  greatest  per  cent,  of  water.  That  mor- 
tars containing  three  parts  sand  to  one  cement  may  be  more 
easily  damaged  by  an  excess  of  water,  is  indicated  by  the  re- 
sults on  Brand  Ln  in  this  table. 

167.    The  effect  on  the  strength  of  Portland  cement  mortars, 


CONSISTENCY   OF  MQXTAR 


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AND  CONCRETE 


of  variations  in  consistency,  has  been  investigated  by  Mr.  Eliot 
C.  Clarke/ M.  Am.  Soc.  C.  E.,  and  by  M.  Paul  Alexandre,2  Chief 
Engineer,  Fonts  et  Chaussees.  The  results  of  one  series  of  ex- 
periments made  by  M.  Alexandre  are  given  in  Table  30.  The 
mortars  were  mixed  with  fresh  water  and  the  samples  immersed 
in  sea  water. 

TABLE   30 

Variations  in  Consistency  of  Mortar 

EFFECT  ON  TENSILE  STRENGTH,  PORTLAND  CEMENT  MORTAR. 

25  pounds  cement  to  1  cu.  ft.  sand  (about  1  to  4  by  weight). 


RESISTANCE,  LBS.  PER  SQ.  IN.  AT  AGE  OF 

WATER 

CONSISTENCY. 

PER 
CENT.  OF 

£ 

>> 

1 

y 

i 

E 

£ 

SAXD. 

& 

% 

0 

9 

0) 

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i 

fl 

ft 

3 

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eo 

t- 

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n 

<N 

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**i 

Dry       .     . 

14 

31 

56 

73 

77 

69 

67 

88 

Disintegrated 

Ordinary  . 

22 

25 

46 

74 

116 

153 

170 

162 

190 

Wet      .     . 

30 

16 

35 

55 

89 

126 

136 

180 

189 

From    "Recherches   Experimentales     sur  Les    Mortiers   Hydrauliques," 
par  M.  Paul  Alexandre,  Annales  des  Fonts  et  Chausse'es,  Sept.,  1890 

It  is  seen  that  the  highest  strength  at  three  days  and  seven 
days  is  given  by  the  dryest  mortar,  at  twenty-eight  days  to  two 
years  by  that  of  the  ordinary  consistency,  and  at  three  years  by 
that  containing  the  highest  per  cent,  of  water.  All  of  the  sam- 
ples exhibited  white  spots  in  the  broken  section  at  three  years, 
and  at  four  years  the  dry  mortar  briquets  had  lost  their  cohe- 
rence on  account  of  their  porosity  permitting  the  sea-water  to 
permeate  them. 

168.  Conclusions.  —  It  may  be  concluded,  then,  that  the 
consistency  of  the  mortar  has  a  very  marked  effect  on  the  ten- 
sile strength  obtained;  that  different  samples  of  cement  are  not 
affected  in  the  same  degree  by  given  variations  in  consistency  ; 
that  the  effect  of  consistency  is  usually  shown  most  plainly  in 
short  time  tests;  and  that  while  the  dryer  or  stiffer  mortars  give 
the  highest  results  on  short  time  tests,  the  moist  mortars  attain 
a  greater  strength  after  a  certain  time. 


1  "Records  of  Tests  of  Cement  made  for  Boston  Main  Drainage  Works.' 
Trans.  A.  S.  C.  E.,  Vol.  xiv. 

2  Annales  des  Fonts  et  Chaussees,  Sept.,  1890. 


TEMPERATURE  103 

169.  Temperature  of  the  Ingredients  and  of  the  Air  where  the 
Briquets  are  Made.  —  The  temperature  of  the  mortar  and  of 
the  air  in  which  the  briquets  are  prepared  is  a  matter  of  some 
moment.     In  1877,  Mr.  Maclay  l  reported  a  series    of  experi- 
ments on   Portland   cements  from   which   conclusions   may  be 
drawn  concerning  the  effects  of  the  temperature  of  the  mortar. 
These  experiments  indicate  that  mortar  having  a  temperature 
of  40°  Fahr.  when  gaged,  will  attain  greater  strength  in  from 
seven  days  to  three  weeks  than  a   mortar    having  an   initial 
temperature  of  70°  Fahr.     One  is  most  likely  to  work  some- 
where between  these  two  temperatures,  but  it  may  be  mentioned 
that    according  to  Mr.  Maclay's  experiments,  it  appears  that 
mortars  gaged  at  a  temperature  of  90°  or  100°  Fahr.   also  at- 
tain a  higher  strength  than  those  gaged  at  70°  Fahr. 

Similar  experiments  made  by  M.  Candlot2  indicate  that  mor- 
tars gaged  with  cold  water  give  but  feeble  resistance  at  first, 
but  in  from  two  weeks  to  one  month,  such  mortars  surpass  in 
strength  those  gaged  with  warm  water.  M.  P.  Alexandre  3  im- 
mersed some  briquets  at  a  temperature  of  about  90°  C.  (194° 
Fahr.)  for  forty-eight  hours  and  then  at  15°  to  18°  C.  (60°  to 
65°  Fahr.)  until  broken,  while  other  briquets  were  maintained 
at  the  latter  temperature  from  the  time  of  molding.  The  bri- 
quets that  were  broken  at  the  age  of  four  days  showed  that 
the  highest  strength  had  been  obtained  by  the  briquets  which 
had  been  kept  hot  for  forty-eight  hours,  but  at  twenty-eight 
days  and  three  months  those  briquets  which  had  not  been  sub- 
jected to  this  high  temperature  gave  the  highest  strength. 

170.  Table  31  gives  a  few  of  the  many  experiments  on   this 
point  made  under  the  author's  direction.     It  appears  that  the 
briquets  made  in  a  low  temperature  (34°  to  37°  Fahr.)  are  usu- 
ally stronger  than  those  made  in  the  ordinary  temperature  of 
65°  to  68°  Fahr.     In  some  cases  the  difference  was  not  very 
great,  and  in  some  of  the  tests  the  briquets  made  in  the  ordi- 
nary temperature  gave  higher  results  at  one  day  and    seven 
days  than  those  made  in  the  cold;  but  at  twenty-eight  days  the 
cold-made  briquets  were  nearly  always  in  the  lead,  and  in  many 

1  "Notes  and  Experiments  on  the  Use  and  Testing  of  Portland  Cement," 
Trans.  A.  S.  C.  E.,  Vol.  vi,  p.  311. 

2  "Ciments  et  Chaux  Hydrauliques" 

3  "Les  Mortiers  Hydrauliques." 


104 


CEMENT  AND  CONCRETE 


Temperature  of  Materials  and  of  Air  where  Made.  Effect  on  Tensile  Strength,  Natural 
and  Portland  Cements 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

a* 

PQ 

1 

0" 

PQ 

o 
§> 

1 
£ 

•pt°o 

•••$•; 

NOTES:  —  All  briquets  made  by  same  molder;  each  result  is  mean  of  five  to  ten  specimens. 
Results  in  columns  headed  "warm,"  temperature  of  materials  used  and  air  where  made  =  65°  to  67°  Fahr. 
Results  in  columns  headed  "cold,"  temperature  of  materials  used  and  air  where  made  =  34°  to  37°  Fahr. 
a.  In  damp  closet  36  hours,  except  1  day  specimens  which  were  12  hours  in  air  where  made  and  12  hours 
in  damp  closet. 
b.  In  damp  closet  24  hours,  except  1  day  specimens  which  were  24  hours  in  air  where  made. 
c.  In  damp  closet  19  to  21  hours,  except  1  day  specimens  which  were  3  to  5  hours  in  air  where  made, 
0  to  1\  hours  in  damp  closet  and  16^  to  21  hours  in  tank. 

.      .      .<N     .     . 

»»A 

•      •      •  t~      •      • 

.      .      .<N      .      . 

6  Months. 

WO 

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3  Months. 

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T»H  00  ^  O  O  CO 

28  Days. 

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CO  CO  rH  rH  <M  rH 

3*1:0  ox  OS-OS  zxHvnft 

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CO   -j     ,_,   -     rH   - 
1                         1 

MORTAR  MIXING  105 

cases  this  difference  held  good  at  three  months  and  six  months. 
Some  of  the  results  indicated  that  if  the  briquets  were  allowed 
to  remain  twenty-four  hours  or  more  in  the  cold  air,  it  tended 
to  counteract  the  beneficial  effects  of  cold  molding,  but  this 
point  was  not  satisfactorily  established. 

171.  From   the  foregoing  the  following  conclusions   may  be 
drawn:  To   make   briquets   of   cold   materials   and   allow   them 
to  remain  some  hours  in  cold  air,  retards  the  hardening  of  the 
briquets;  but  when  briquets  so  treated  are,  after  a  few  hours, 
placed  in  a  medium  of  ordinary  temperature,  they  gain  strength 
more  rapidly  than  briquets  made  of  warm  materials  and  kept 
continuously  at   the  ordinary  temperature  of  60°  to  70°  Fahr. 
After  being  placed  in  a  warmer  medium,   the  briquets   made 
with  cold  materials  in  cold  air  frequently  gain  strength  at  such 
a  rate  as  to  surpass  in  strength  the  warm-made  briquets  at  seven 
days;  the  former  almost  invariably  surpass  the  latter  at  twenty- 

^ight  days.  In  some  cases  it  appears  that  this  superiority  of 
cold-made  briquets  is  maintained  up  to  six  months,  but  in  other 
cases  the  difference  seems  to  disappear  after  three  months. 

Although  these  variations  in  temperature  have  not  as  marked 
an  effect  on  tensile  strength  as  have  many  other  variations  in 
manipulation,  yet  in  carefully  conducted  experiments  one  should 
always  operate  in  a  constant  temperature.  As  a  matter  of 
convenience,  65°  to  70°  Fahr.  will  commend  itself,  and  this 
temperature  may  well  be  taken. 

172.  GAGING  BY  HAND.  —  The  objects    to    be    attained    in 
gaging  are  to  thoroughly  incorporate  the  cement  and  sand,  to 
evenly  distribute  the  water  throughout  the  mass,  and,  if  pos- 
sible, to  give  the  mortar  a  certain  tenacity  resembling  that  of 
putty.     This  last  object  is  not  always  possible  of  attainment 
with  mortars  containing  a  large  dose  of  sand. 

The  ordinary  method  of  preparing  mortars  in  the  laboratory 
is  to  gage  with  a  trowel  on  a  glass,  slate,  or  marble  slab.  In 
gaging  mortars,  the  cement  and  sand  are  first  mixed  dry;  the 
materials  are  then  drawn  away  from  the  center,  leaving  a  crater 
to  receive  the  water,  which  is  all  added  at  one  time.  The  dry 
material  is  then  gradually  turned  from  the  edges  toward  the 
center  until  all  of  the  water  is  absorbed,  after  which  the  mass 
is  thoroughly  worked  with  the  trowel  in  such  a  way  as  to  rub 
the  material  between  the  trowel  and  plate  until  the  consistency 


106  CEMENT  AND  CONCRETE 

is  uniform  throughout.  A  batch  of  mortar  sufficient  for  five 
briquets  cannot  usually  be  properly  gaged  by  this  method  in 
less  than  five  minutes. 

The  Committee  of  the  American  Society  of  Civil  Engineers, 
in  their  preliminary  report  on  methods  of  manipulation,  sug- 
gested that  "as  soon  as  the  water  has  been  absorbed,  which 
should  not  require  more  than  one  minute,"  the  mortar  should 
be  kneaded  with  the  hands  for  one  and  one-half  minutes,  the 
process  being  similar  to  that  used  in  kneading  dough. 

173.  HOE  AND  BOX  METHOD.  —  Mr.  Alfred  Noble  used  for 
many  years  a  form  of  gaging  apparatus,  consisting  of  a  box 
with  sloping  bottom,  in  which  the  mortar  is  worked  by  means 
of  a  hoe.  The  author  has  used  an  iron  box  made  on  this  prin- 
ciple (Fig.  2),  which  has  given  excellent  results.  The  box  is 
2  feet  7^  inches  long,  6  inches  wide  at  the  bottom,  and  at  the 


"°^v> 

\  -j      .-'  f 

L  

—  '-    ?'  8*     -—  •*! 

Side  Elevat/on  End- 

FIG.  2.— MIXING  BOX 

center  is  6  inches  deep.  The  level  part  of  the  bottom  is  3  inches 
by  6  inches,  and  from  this  level  part  the  inclined  portions  of 
the  bottom  slope  up  toward  the  ends  at  an  inclination  of  about 
22J  degrees.  The  sides  of  the  box  extend  below  these  in- 
clined planes  to  give  a  level  bearing  for  the  box  when  in  use. 
It  is  also  well  to  have  the  sides  flare  enough  to  give  a  width 
of  6^  inches  at  the  top  to  prevent  the  hoe  from  becoming 
wedged.  A  "  German  clod  hoe,"  which  is  strong  and  heavy, 
yet  a  trifle  flexible  in  the  blade,  is  used  in  connection  with  the 
box. 

The  weighed  quantities  of  the  dry  ingredients  being  put  in 
the  box  and  well  mixed,  the  measured  volume  of  water  is  added. 
Two  minutes  of  hard  work,  in  which  the  operator  may  put  all 
his  strength,  is  sufficient  to  bring  the  mass  to  plasticity  if  the 
amount  of  water  added  is  correct.  A  return  to  the  trowel  and 


/     MORTAR  MIXING  107 

slab  method  of  mixing  is  not  likely  after  a  trial  of  this  simple 
device. 

174.  MACHINE  FOR  MORTAR  MIXING.  —  As  the  mixing  by 

hand  is  a  rather  slow  and  tedious  method,  and  the  hoe  and  box 
method  are  not  very  generally  known,  several  machines  have 
been  devised  to  do  the  work.  None  of  them,  however,  has 
given  such  satisfactory  results  as  to  bring  it  into  general  use. 

One  of  the  machines  is  called  a  "jig,"  or  "milk  shake" 
machine,1  and  consists  of  a  cup  which  moves  rapidly  up  and 
down,  this  motion  being  imparted  by  means  of  a  hand  wheel, 
crank  and  connecting  rod.  The  dry  cement  and  water  being 
placed  in  the  cup  and  tightly  covered,  a  few  rapid  turns  of  the 
wheel  are  sufficient  to  reduce  the  cement  to  a  paste.  This 
form  is  only  applicable  to  neat  cement  mortars,  and  has  been 
said  to  give  unsatisfactory  results  even  for  these,  though  in 
some  laboratories  this  machine  has  been  used  for  all  neat 
mortars. 

Other  forms  have  been  made  in  which  the  mortar  is  thoroughly 
stirred  by  means  of  forks  or  blades  projecting  into  the  mortar 
from  a  horizontal  arm  above.  The  gager  devised  by  Mr.  Faija 
is  constructed  on  this  principle,  and  similar  machines  may  be 
obtained  from  manufacturers  of  testing  apparatus. 

175.  Steinbriich's  Mortar  Mixer   is  a  German  machine  oper- 
ating on  a  different  principle.     It  consists  of  a  circular  shell 
having  on  its  upper  side  and  near  its  outer  edge  a  circular  groove, 
or  trough,  to  receive  the  mortar  to  be  mixed.     In  this  trough 
rests  a  wheel  on  a  fixed  horizontal  axis,  which  is  above  the  pan 
and  normal  to  the  axis  of  the  pan.     A  cross-section  of  the  rim 
of  the  wheel  is  a  semicircle  fitting  the  groove  in  the  pan.     The 
gearing  is  such  that  the  pan  is  made  to  revolve  about  its  vertical 
axis,  and  the  wheel  about  its  horizontal  axis,  the  inner  surface 
of  the  trough  and  the  under  side  of  the  periphery  of  the  wheel 
where  the  two  are  in  contact  moving  in  the  same  direction  at 
a  given  instant.     The  mortar  is  thus  rubbed  between  the  two. 
Small  blades,  or  plows,  scrape  the  sides  of  the  trough  as  the  latter 
revolves,  thus  keeping  the  mortar  in  the  bottom  of  the  trough. 
The  wheel  and  the  plows  are  mounted  on  hinged  axes,  or  sup- 
ports, so  that  they  may  be  raised  from  the  pan  when  the  mortar 


1  S.  Bent  Russell,  Engineering  News,  Jan.  3,  1891. 


108 


CEMENT  AND  CONCRETE 


is  to  be  cleaned  out.     The  mixing  requires  about  two  and  one- 
half  minutes.     The  price  of  the  machine  is  about  $130. 

176.  The  amount  of  gaging  which  a  mortar  receives  has  an 
important  effect  on  its  consistency  and  the  strength  it  will 
attain.  This  was  found  to  be  the  case  in  several  experiments 
where  mortar  gaged  eight  minutes  in  the  box  described  above, 
gave  from  15  to  35  per  cent,  greater  strength  at  one  year  than 
that  which  was  gaged  but  two  minutes,  the  amount  of  water 
used  being  the  same  in  the  two  cases.  Experiments  on  this 
point  are  given  in  Table  78,  §  364.  It  is  therefore  important  to 
eliminate,  if  possible,  the  variations  which  must  follow  hand 
mixing,  but  as  yet  no  apparatus  has  seemed  to  meet  with  gen- 


FlG.  3.  — FORM  OF  BRIQUET 
USED  ON  THE  CONTI- 
NENT OF  EUROPE. 


FIG.  4.  — FORM  OF  BRIQUET 
USED    IN    THE    UNITED 
STATES. 


eral  approval,  though  among  machine  mixers  those  similar  to 
that  used  by  Mr.  Faija  seem  to  have  given  the  best  results. 
The  hoe  and  box  method  described  in  §  173  partially  eliminates 
the  personal  equation,  and  for  facility  of  operation  and  thor- 
oughness of  mixing  leaves  little  to  be  desired. 

177.  FORM  OF  BRIQUET.  —  The  shape  and  size  of  the  briquet 
have  been  the  subject  of  much  discussion  and  experiment. 
Mr.  John  Grant,  a  pioneer  in  tensile  tests,  tried  many  forms 
before  finally  adopting  one  quite  similar  to  the  form  afterward 
recommended  by  the  Committee  of  the  Amer.  Soc.  C.  E.  in 
1885.  Mr.  Alfred  Noble  also  made  a  series  of  experiments  on 


FORM  OF  BRIQUET  109 

different  styles  of  molds  and  clips,  and  presented  the  results 
in  a  paper  read  before  the  American  Society  of  Civil  Engineers.1 

There  are  two  forms  of  mold  that  are  now  in  quite  general 
use.  On  the  continent  of  Europe  the  form  most  generally  used 
is  that  shown  in  Fig.  3.  It  has  a  cross-sectional  area  of  five 
square  centimeters  (.775  sq.  in.)  at  the  smallest  place,  and  the 
heads  of  the  briquet  are  elliptical  in  form,  the  major  axes  being 
transverse  to  the  briquet  axis.  The  curve  forming  the  side  of 
the  briquet  in  the  central  portion  is  of  very  short  radius,  giving 
the  effect  of  a  semicircular  notch  on  either  side  of  the  briquet 
at  the  smallest  section.  These  notches  have  the  effect  of  con- 
fining the  break  to  this  place. 

The  other  form  of  mold  is  the  one  mentioned  above  as  recom- 
mended by  the  Amer.  Soc.  C.  E.  Committee,  and  used  in  America 
and  England.  A  briquet  of  this  form  is  shown  in  Fig.  4.  The 
cross-sectional  area  at  the  center  is  one  square  inch,  and  the 
increase  of  section  toward  the  ends  is  gradual,  the  radius  of  the 
curve  at  the  side  of  the  briquet  being  J  inch. 

178.  Area  of  the  Breaking  Section.  —  Formerly  a  section  of 
2}  square  inches  was  more  commonly  used  here  and  in  England, 
while  an  area  of  16  square  centimeters  (2.48  sq.  in.)  was  com- 
mon in  France  and  other  continental  countries.  The  larger 
the  area  of  the  breaking  section,  the  smaller  will  be  the  com- 
puted strength  per  square  inch;  this  point  seems  fairly  well 
established,  although  the  experiments  recorded  in  a  very  ex- 
cellent paper  by  Mr.  Eliot  C.  Clarke  2  indicate  no  apparent  dif- 
ference in  strength  between  briquets  1  square  inch  and  2J 
square  inches  in  section. 

M.  Durand-Claye  found  that  the  tensile  strength  of  a  briquet 
varied  more  nearly  as  the  perimeter  than  as  the  area  of  the 
section.  The  experiments  of  M.  Candlot  do  not  point  to  this 
conclusion,  though  they  clearly  show  that  the  indicated  strength 
per  square  centimeter  is  very  much  greater  for  a  briquet  hav- 
ing an  area  of  five  square  centimeters  at  the  small  section  than 
for  a  briquet  of  16  square  centimeters  area. 

Mr.  D.  J.  Whittemore 8  experimented  with  briquets  that  were 


1  Trans.  Amer.  Soc.  C.  E.,  Vol.  ix,  p.  186. 

2  Trans.  Amer.  Soc.  C.  E.,  Vol.  xiv,  p.  141. 

3  "Tensile  Tests  of  Cements,"  etc.     Trans.  A.  S.  C.  E.,  Vol.  ix,  p.  329. 


110  CEMENT  AND  CONCRETE 

circular  in  cross-section.  He  found  that  while  the  ultimate 
strength  of  a  briquet  was  about  proportional  to  the  periphery 
of  the  breaking  section  for  the  ordinary  solid  briquet,  yet  if  a 
core  were  inserted  in  the  mold,  giving  the  cross-section  an  annu- 
lar form,  this  proportion  was  not  maintained.  It  was  con- 
cluded from  this  that  the  apparent  peripheric  strength  could 
not  be  explained  by  saying  that  the  surface  of  the  briquet  had 
gained  a  greater  strength  than  the  interior,  but  that  the  expla- 
nation must  rather  be  sought  in  the  method  of  applying  the 
stress  in  breaking  the  briquet.  The  force  being  communicated 
to  the  surface  of  the  briquet,  the  stress  is  not  uniformly  dis- 
tributed throughout  the  breaking  section,  because  of  the  low 
elasticity  of  the  mortar. 

M.  Paul  Alexandre  showed  that  the  difference  in  strength 
per  unit  area  decreased  with  age,  although  it  did  not  entirely 
disappear  at  one  year.  It  would  therefore  seem  that  the  expla- 
nation of  this  phenomenon  may  be  found  in  a  combination  of 
these  two  causes;  more  rapid  hardening  of  the  smaller  speci- 
mens, and  greater  inequality  of  stress,  in  breaking  the  briquets 
of  larger  section. 

179.  Form  of  Briquet  Suggested.  —  As  a  result  of  experi- 
ments which  will  be  described  under  the  head  of  "  Clips,"1 
(Art.  25)  the  following  conclusions  were  drawn  as  to  the  desir- 
able features  for  a  briquet: 

1st.  The  smallest  section  should  not  have  an  area  much  less 
than  one  square  inch.  Probably  an  area  of  five  square  centi- 
meters would  represent  a  minimum. 

2d.  The  area  of  the  section  of  the  briquet  between  opposite 
gripping  points  should  be  about  one  and  three-fourths  times 
the  area  of  the  smallest  section. 

3d.  The  distribution  of  stress  over  the  smallest  section 
should  be  as  nearly  uniform  as  possible. 

4th.  The  curve  of  the  sides  at  the  breaking  section  should 
not  be  very  sharp;  one-half  inch  might  be  taken  as  a  minimum 
radius. 

5th.  The  area  of  the  vertical  section  from  the  gripping  point 
to  the  plane  of  the  end  of  the  briquet  —  the  section  subjected 


1  These  experiments  were  described  by  the  writer  in  detail  in  "Municipal 
Engineering,"  Dec.,  1896,  Jan.  and  Feb.  1897. 


FORM  OF  BRIQUET 


111 


to  shear  when  .the  stress  is  applied  —  should  be  nearly  as  great 
as  the  area  of  the  neck  of  the  briquet. 

6th.    The  face  and  back  of  the  briquet  should  be  parallel 
planes,  to  permit  of  easy  storage. 

7th.    The  total  volume  should  be  kept  as  small  as  is  consis- 
tent with  the  other  conditions. 

Fig.  5  represents  a  form  of  briquet  which  will,  it  is  thought, 
satisfactorily  fulfill  the  above  requirements,  and  in  which  it  is 
believed  the  full  strength  of  the  smallest  section  may  be  more 
nearly  developed  than  with  present  forms.  The  curve  at  the 
central  section  has  a  radius  of  one  inch,  and  the  line  of  the 
side  of  the  briquet  is  con- 
tinued in  a  tangent  one-  ( < 

half  inch  in  length,  having 
an  inclination  of  nearly 
45  degrees  with  the  axis 
of  the  briquet.  The  total 
length  of  the  briquet  is 
four  inches,  the  ends  be- 
ing formed  by  straight 
lines  tangent  to  the  curves 
forming  the  corners.  If 
the  clip  is  so  formed  that 
the  gripping  points  bear 
at  the  centers  of  the  one- 
half  inch  tangents  form- 
ing the  sides  of  the  briquet, 
the  distance  between  op- 
posite gripping  points  will 
be  1-J  inches. 

180.  Comparison  with 
other  Forms.  —  Compar- 
ing this  briquet  with  the  forms  in  common  use,  the  German  and 
the  form  shown  in  Fig.  5  both  have  an  area  between  opposite 
gripping  points  about  If  times  the  area  of  the  smallest  section, 
but  in  the  form  shown  in  Fig.  4  this  ratio  is  too  small  to  fulfill 
the  second  specification. 

The  unequal  distribution  of  stress  over  the  breaking  section 
of  the  briquet  has  already  been  mentioned  as  a  probable  partial 
cause  why  briquets  of  small  cross-section  show  a  greater  strength 


FIG.  5.  — FORM   OF   BRIQUET  SUGGESTED 
FOR   USE 


112  CEMENT  AND  CONCRETE 

per  unit  area  than  those  having  a  larger  area  of  cross-section. 
In  Johnson's  " Materials  of  Engineering"  is  given  the  theory  of 
the  distribution  of  stress  over  the  breaking  section  of  a  briquet, 
as  developed  by  M.  Durand-Claye,  and  published  in  Annales  des 
Pouts  et  Chaussses  of  June,  1895.  Applying  the  formulas  there 
given  to  three  styles  of  briquet,  the  A.  S.  C.  E.  form  of  1885, 
the  German  standard,  and  the  form  shown  in  Fig.  5,  it  is  found 
that  the  ratios  of  the  maximum  stress  to  the  mean  stress  are, 
for  the  three  forms  respectively,  1.54,  1.52  and  1.22.  From  a 
theoretical  point  of  view,  this  means  that  with  a  total  pull  of 
100  pounds  on  each  briquet,  the  outer  fiber  of  the  briquet 
shown  in  Fig.  4  would  be  subjected  to  a  stress  of  154  pounds 
per  square  inch,  while  with  the  form  suggested  above,  the 
stress  on  the  outer  fiber  would  be  but  122  pounds  per  square 
inch  ;  briquets  of  the  latter  form  should,  therefore,  theoretically, 
show  a  breaking  strength  1.27  times  the  strength  given  by 
briquets  of  the  same  mortar  made  in  the  A.  S.  C.  E.  form  of 
1885. 

The  German  form  has  too  sharp  a  curve  at  the  sides  to  fulfill 
the  fourth  requirement  given  above.  All  of  the  forms  comply 
with  the  first,  fifth  and  sixth  requirements. 

As  to  the  volume  of  the  briquet,  the  author's  form  having  a 
total  length  of  four  inches,  has  about  50  per  cent,  greater  volume 
than  the  A.  S.  C.  E.  form  of  1885. 

181.  MOLDS.  —  In  the  early  tests  of  cement,  wooden  molds 
were  employed,  but  they  absorb  water  from  the  mortar  and 
soon  warp  out  of  shape.  Iron  molds  have  also  been  used  to  a 
considerable  extent,  but  these  are  apt  to  become  rusted  if  not 
in  constant  use.  Brass,  bronze  or  some  similar  metal  not  easily 
corroded  should  be  used,  and  molds  of  this  character  can  be 
obtained  of  dealers  in  testing  apparatus. 

The  molds  may  be  made  single,  or  in  " nests"  or  "gangs" 
of  three  to  five.  The  two  halves  of  the  mold  may  be  entirely 
separable,  or  may  be  hinged  at  one  end  and  fastened  by  a  clip 
at  the  other  end.  The  gang  molds  are  somewhat  cheaper  than 
the  single  ones.  The  hinged  molds  and  those  held  with  patent 
clip  are  rather  difficult  to  clean,  while  the  gang  molds,  if  made 
heavy  enough  to  prevent  spreading,  are  unwieldy,  and  briquets 
are  removed  from  them  with  greater  difficulty  than  from  the 
single  molds.  It  is  considered,  therefore,  that  the  most  con- 


MOLDING  BRIQUETS  113 

vcnicnt  form  is  the  single  mold,  in  which  the  two  halves  are 
held  together  by  a  screw  clamp  of  simple  design. 

182.  To  clean  these  molds,  place  ten  in  a  row  with  clamps 
removed  ;  scrape  the  upper  faces  with  a   piece  of  zinc,  brush 
with  a  stiff  "  horse-brush/'   and  wipe  with  oily  waste.     Turn 
them   over   and   repeat   the   process.     Then   separate   the   two 
halves  of  each  mold,  place  the  twenty  halves  in  line  with  inner 
surfaces  up,  forming  a  trough  twenty  inches  long.     Wipe  this 
trough  thoroughly  with  oily  waste,  finishing  with  some  that  is 
only  slightly  oiled. 

183.  MOLDING.  —  Methods  of  molding  briquets  vary  widely 
and  have  a  considerable  effect  on  the  results  obtained  by  differ- 
ent operators.     The  mold  may  be  placed  on  a  glass  or  marble 
slab,  or   on   a   porous   bed.     This   difference   in   treatment   will 
affect  the   results   chiefly   because   a   porous   bed   will   extract 
moisture  from  the  briquet,  and,  unless  it  is  already  mixed  very 
dry,  will  make  it  give  a  higher  result  on  a  short  time  test.     The 
use  of  a  porous  bed  probably  originated  with  a  desire  to  more 
closely  imitate  the  use  of  mortar  in  actual  work,  but  it  intro- 
duces another  source  of  variation  in  results  and  should  not  be 
followed. 

184.  In  hand    work  the  whole  mold  may  be  filled  at  once, 
or  small  amounts  of  mortar  may  be  added  at  a  time,  and  each 
layer  packed;  the  mortar  may  be  tamped  into  the  mold  with  a 
rod,  in  which  case  the  pressure  used  may  vary  widely;  or  the 
mortar  may  be  pressed  in  with  the  fingers,  or  with  the  point  of 
a  small  trowel;  and,  finally,  the  pressure  applied  on  the  top  of 
the  whole  briquet  may  be  light  or  heavy.     It  is  evident  that  it 
is  almost  impossible  to  so  describe  all  these  details  of  manipula- 
tion that  another  operator  may  follow  the  same  system  and 
obtain  the  same  results.     The  practice  of  ramming  the  mortar 
into  the  mold  by  means  of  a  metal  rod  or  a  stick  faced  with 
zinc  is  objectionable,  because  of  the  possible  wide  variation  in 
the  force   thus  applied.     This   method  is  sometimes   used   by 
manufacturers,  since  by  making  the  mortar  quite  dry  and  ram- 
ming it  into  the  molds  very  hard,   a  high  initial  strength   is 
obtained.     But  the  foremost  cement  makers  are  now  eschewing 
such  methods  and  are  aiming  to  make  fair  tests.     Some  experi- 
ments   made    under   the   author's   direction   indicate   that   the 
pressure  applied  to  the  top  of  the  briquet  is  the  salient  point  in 


114 


CEMENT  AND  CONCRETE 


the  process  of  molding,  and  that  the  other  details  are  of  minor 
importance. 

In  Germany  a  heavy  trowel  or  iron  plate  weighing  about 
250  grams,  and  provided  with  a  handle,  is  used  in  making  one- 
to-three  mortar  briquets.  The  mortar  is  made  rather  dry 
(about  10  per  cent,  water),  and  after  the  mold  is  filled  and 
heaped,  the  mortar  is  beaten  with  the  trowel  until  it  becomes 
elastic,  and  water  appears  on  the  surface.  The  excess  of  mor- 
tar is  then  scraped  off  with  an  ordinary  trowel  or  spatula. 

185.  Several  machines  have  been  devised  for  making  bri- 
quets, some  of  which  are  said  to  give  good  results.  Among 
these  the  most  prominent  is  the  Bohme  hammer  apparatus, 
which  is  much  used  in  Germany,  although  not  employed  to  any 
extent  in  the  United  States.  It  consists  of  a  plunger  which 
fits  the  mold  and  upon  which  a  given  number  of  blows  are 
struck  by  a  hammer.  The  mortar  is  first  gaged  as  for  hand 
molding,  and  placed  in  the  form.  A  pinion,  turned  by  a  hand 
crank,  is  geared  to  a  wheel  provided  with  ten  cams.  These 
cams  operating  on  the  wrought  iron  handle  of  the  hammer 
cause  a  certain  number  of  blows  to  be  delivered  to  the  plunger. 
The  mechanism  is  automatically  shut  off  after  the  proper  number 
of  blows  has  been  delivered.  The  following  results  were  ob- 
tained by  Professor  Bohme  with  his  apparatus:  — 

TABLE  32 

Comparison  of  Hand  Made  Briquets  with  Those  Made  by  Bohme 

Hammer 


MEAN  TENSILE 

No. 

METHOD. 

WEIGHT  OF 
BRIQUETS. 

STRENGTH  AT 
7  DAYS  IN  KGS. 

PER  SQ.  CM. 

1 

By  hand 

160.0 

16  06 

2 

Hammer,    75  blows 

158.0 

12.75 

3 

100     " 

159.5 

13.25 

4 

"         125     " 

159.5 

14.56 

5 

"         150     " 

159.0 

1556 

186.  Several  American  engineers  have  devised  machines  for 
briquet-making,  but  none  of  them  has  been  generally  adopted. 

An  apparatus  designed  by  Prof.  Charles  Jameson,  of  Iowa 
University,  is  said  to  work  very  rapidly.  The  mortar  is  packed 
in  the  mold  by  a  plunger  of  the  form  of  the  briquet.  This 


MOLDING  BRIQUETS  115 

plunger  works  in  a  chamber  of  the  same  shape  as  the  briquet 
mold.  The  mortar  is  placed  in  a  hopper  at  the  side  of  this 
chamber,  and  is  delivered  to  the  mold  automatically  when  the 
plunger  is  raised.  The  force  is  applied  to  the  plunger  by  hand, 
but  it  should  be  so  arranged  that  this  be  done  by  a  weight,  to 
prevent  variations  in  pressure.  In  this  method  the  briquet  is 
removed  from  the  mold  as  soon  as  made,  and  this  would  appear 
to  be  an  objectionable  feature. 

Professor  Spalding,  of  Cornell  University,  in  his  excellent 
little  book  on  "Hydraulic  Cement,"  states  that  he  has  found 
that  "a  pressure  of  about  500  pounds  upon  the  surface  of  the 
briquet  is  sufficient  to  produce  a  compact  and  homogeneous 
briquet,  and  a  crude  appliance  consisting  of  a  lever  arranged  to 
bring  a  pressure  upon  the  mortar  in  the  mold  by  means  of  a 
weight  suspended  at  the  end  of  the  lever,  has  been  found  to 
increase  both  the  rapidity  and  the  regularity  of  the  work,  and 
especially  to  diminish  the  variations  in  results  obtained  by  dif- 
ferent men." 

A  machine  which  would  give  more  uniform  results  and  work 
more  rapidly  than  hand  molding,  would  commend  itself  for 
general  use. 

187.  Method  Recommended.  —  In  making  briquets  by  hand, 
the  mortar  may  well  be  packed  into  the  molds  by  the  fingers, 
which  should  be  protected  by  rubber  tips.     When  the  mold  is 
filled  and  slightly  heaped,  the  trowel  should  be  placed  on  top, 
and  the  molder  put  about  60  pounds  pressure  on  the  trowel. 
The  excess  mortar    is  then  cut  off  by  the  trowel  and  the  top  of 
the  briquet  is  smoothed  by  drawing  the  trowel  across  the  face. 
The  results  obtained  by  four  molders  using  this  method  in  the 
same  laboratory  are  given  in  Table  33. 

188.  The  recent  progress  report  of   the  Committee  of  the 
American  Society  of  Civil  Engineers  on  uniform  tests  of  cement 
contains  the  following,  under  " Molding":  — 

"  Having  worked  the  paste  or  mortar  to  the  proper  consist- 
ency, it  is  at  once  placed  in  the  molds  by  hand. 

"The  Committee  has  been  unable  to  secure  satisfactory  re- 
sults with  the  present  molding  machines;  the  operation  of 
machine-molding  is  very  slow,  and  the  present  types  permit  of 
molding  but  one  briquet  at  a  time,  and  are  not  practicable  with 
the  pastes  or  mortars  herein  recommended. 


116 


CEMENT  AND  CONCRETE 


TABLE   33 
Results  Obtained  by  Different  Molders  when  Using  Similar  Mortar 


X 

. 

MEAN  TENSILE 

c  M 

o 

o     r 

o  w 

STRENGTH. 

gw 

H 
w 

^r 

si 

^O  r,  fd 

^ 

II 

pa 

H 

i 

M 

K 

fcO 

l3p 

H  H 

•^  63 

-  H 

AGE. 

M 

M 

H 
A 

DATE. 

m 

H 

PH 

pj  Wfl 

W  SB 

Q 

Q 

Q 

K  "' 

W 

jsj 

fc  fc 

w  ^ 

PH  tj 

_j 

33  ^ 

K 

rH 

H       ^ 

s 

O 

0 

0 

JB  K 

CO 

£   « 

^1 

* 

S 

S 

P 

a 

6 

c 

d 

e 

/ 

9 

/I 

i 

1 

0 

31.6 

62-65 

1  days 

81 

92 

89 

5 

10-22 

Clear 

2 

0 

'4 

K 

28     " 

197 

213 

220 

5 

3 

1 

18.7 

67-62 

7     " 

79 

91 

89 

5 

4 

1 

*« 

»» 

28     " 

235 

257 

259 

5 

5 

1 

« 

63-68 

3  mo. 

515 

541 

519 

5 

6 

1 

" 

" 

1  year 

558 

569 

555 

5 

7 

2 

15.2 

70-65 

28  days 

196 

186 

197 

5 

8 

2 

u 

u 

3  mo. 

423 

383 

406 

5 

9 

3 

13.8 

65-61 

3  mo. 

253 

263 

239 

5 

10 

3 

" 

» 

1  year 

260 

232 

236 

5 

11 

Sum  of  Means 

2797 

2827 

2809 

Molder 

Molder 

S. 

T. 

12 

0 

31.6 

62-65 

7  days 

60 

60 

5 

10-28 

Cloudy 

13 

0 

*« 

" 

28     » 

145 

167 

5 

14 

1 

18.7 

65 

7     " 

. 

67 

71 

5 

15 

1 

" 

«« 

28     «' 

, 

223 

211 

5 

16 

1 

1  1 

" 

3  mo. 

, 

435 

449 

5 

17 

1 

K 

" 

1  year 

. 

504 

491 

5 

18 

2 

152 

67 

28  days 

. 

182 

179' 

5 

19 

Sum  of  Means 

• 

1616 

1628 

Cement,  Brand  Gn,  Sample  21  R.     Sand,  Crushed  Quartz  20  to  40. 
All  briquets  in  same  line  received  same  treatment  after  made  and   were 
immersed  in  same  tank  until  broken. 
1   Mean  of  ten  specimens. 

"Method.  The  molds  should  be  filled  at  once,  the  material 
pressed  in  firmly  with  the  fingers  and  smoothed  off  with  a 
trowel  without  ramming;  the  material  should  be  heaped  up  on 
the  upper  surface  of  the  mold,  and,  in  smoothing  off,  the  trowel 
should  be  drawn  over  the  mold  in  such  a  manner  as  to  exert  a 
moderate  pressure  on  the  excess  material.  The  mold  should  be 
turned  over  and  the  operation  repeated. 

"A  check  upon  the  uniformity  of  the  mixing  and  molding  is 
afforded  by  Weighing  the  briquets  just  prior  to  immersion,  or 


STORING  BRIQUETS 


117 


upon  removal  from  the  moist  closet.  Briquets  which  vary  in 
weight  more  than  3  per  cent,  from  the  average  should  not  be 
tested." 

189.  Marking  the  Briquets.  —  The  briquets  made  in  a  given 
laboratory  should  be  numbered  consecutively,  so  that  no  con- 
fusion can  arise,  and  this  one  number  is  all  that  should  be  placed 
on  the  briquet.     The  record  of  the  brand  of  cement,  the  pro- 
portions used,  etc.,  should  be  placed  in  a  book  opposite  the 
briquet   number.     The   briquets   should   be   numbered   on   the 
face,   near  the  end.     Steel  stamps  furnish  a  ready  means  of 
numbering,  and  when  mortar  contains  more  than  two  parts  of 
sand  to  one  of  cement  a  thin  strip  of  neat  cement  paste  plastered 
across  one  end  of  the  briquet  will  aid  in  making  the  numbers 
legible. 

ART.  24.     STORING  BRIQUETS 

190.  The  Time  in  Air  before  Immersion.  —  As  soon  as  the 
briquets  are  molded  they  should  be  covered  with  a  damp  cloth 

TABLE  34 

Variations  in  Length  of  Time  Briquets  are  Left  in  Moist  Air  before 
Immersion  —  Natural  Cement 


TENSILE  STRENGTH,  POUNDS  PER 

SQ.  INCH. 

CEMENT. 

PARTS  CRUSHED 
QUART/,  20-30° 

TO 

1  OEMKNT 

AGE 
WHEN 
BROKEN. 

HOURS  IN  MOIHT  AIR  BEFORE 
IMMERSION. 

8 

12 

24 

48 

72 

168 

Brand. 

Sample. 

Gn 

15  K 

0 

7  days 

123 

139 

151 

161 

237 

t  1 

1 

7  days 

91 

. 

106 

114 

114 

182 

16  R 

0 

28  days 

110 

106 

109 

89 

113 

1 

28  days 

142 

. 

138 

139 

152 

175 

2 

28  days 

102 

105 

112 

113 

115 

An 

G 

0 

7  days 

168 

181 

194 

185 

238 

0 

28  days 

. 

200 

210 

224 

241 

243 

1 

7  days 

108 

137 

141 

157 

160 

1 

28  days 

278 

283 

297 

297 

301 

3 

28  days 

120 

130 

137 

139 

152 

NOTE  :  —  All  briquets  made  by  same  molder.     Each  result  is  mean  of  ten 
specimens. 

until  they  are  ready  to  be  removed  from  the  molds,  when  they 
should- be  transferred  to  a  "damp  closet,"  lined  with  zinc  or 
other  non-corroding  metal.  It  was  formerly  the  practice  to 
immerse  the  briquets  as  soon  as  they  were  considered  to  be 


118 


CEMENT  AND  CONCRETE 


sufficiently  set;  but  for  the  sake  of  uniformity,  they  are  now 
left  in  moist  air  for  twenty-four  hours  before  immersion,  whether 
the  cement  is  quick  or  slow  setting.  Briquets  which  are  to  be 
broken  at  twenty-four  hours,  however,  are  usually  immersed 
as  soon  as  set  hard. 

Table  34  gives  the  results  obtained  by  allowing  natural 
cement  briquets  to  remain  in  moist  air  different  lengths  of  time 
before  immersion.  In  general,  the  strength  is  greater  for  seven 
and  twenty-eight  day  tests  the  longer  the  briquets  are  allowed 
to  remain  in  the  moist  air.  It  appears  that,  while  the  time  in 
moist  air  should  be  made  as  nearly  uniform  as  possible,  a  varia- 
tion of  a  few  hours  will  not  cause  an  important  difference  in 
strength. 

TABLE   35 
Gain  or  Loss  in  Strength  of  Natural  Cement  Briquets  by  Immersion 


TENSILE  STRENGTH,  POUNDS 

PER  SQ.  INCH. 

TIME  IN 
MOIST  AIR. 

TIME  IN  TANK. 

AGE   \\  H  K  N 

BROKEN. 

One  Part  Stand- 

Neat Cement. 

ard  Sand  to 

One  Cement. 

20  hours 

20  hours 

151 

94 

18  hours 

6^  days 

7  days 

147 

153 

2  days 

2  days 

192 

126 

2  days 

5  days 

7  days 

160 

158 

3  days 

3  days 

*205 

141 

3  days 

4  days 

7  days 

177 

155 

4  days 

. 

4  days 

218 

165 

4  days 

3  days 

7  days 

191 

165 

5  days 

.... 

5  days 

230 

175 

5  days 

2  days 

7  days 

192 

169 

NOTE  :  —  All  briquets  made  by  same  molder.  Each  result  is  mean  of 
five  specimens. 

Table  35  shows  the  early  action  of  the  water  on  the  briquets. 
These  tests  were  made  in  sets  of  ten;  five  briquets  of  a  set  were 
immersed  after  twenty  hours,  forty-eight  hours,  etc.,  while  the 
other  five  of  the  same  set  were  broken  at  the  time  the  first  five 
were  immersed.  With  this  sample  of  natural  cement,  it  appears 
that  the  briquets  lose  part  of  their  strength  by  immersion,  and 
that  some  time  is  required  to  regain  this  lost  strength.  Thus, 
with  neat  cement  mortar  the  briquets  broken  at  twenty  hours 
without  immersion  were  as  strong  as  those  broken  at  seven 
days  which  had  been  immersed  the  last  six  and  one-fourth  days. 
With  briquets  of  one-to-one  mortar,  it  appears  that  if  immersed 


STORING  BRIQUETS  119 

at  the  end  of  four  days,  the  gain  in  strength  during  the  last 
three  days  (in  water)  is  about  equal  to  the  loss  of  strength  due 
to  immersion.  If  immersed  earlier  than  this,  the  gain  is  greater 
than  the  loss,  but  if  immersed  later,  the  loss  is  greater  than 
the  gain. 

191.  For   storing   briquets   the   required   twenty-four    hours 
before  immersion  a  moist  closet  is  very  convenient,  tends  to 
promote    uniformity    of    treatment,    and    may    be    very   easily 
made.     The  use  of  a  damp  cloth  for  covering  briquets  is  incon- 
venient, as  the  cloth  may  dry  out.     If  it  is  used,  the  end  of 
the  cloth  should  rest  in  a  pail  of  water,  so  it  will  keep  wet  by 
capillarity;  it  should  also  be  kept  from  touching  the  briquets  by 
a  wire  screen  or  by  wooden  slats. 

A  moist  closet  may  be  made  of  slate,  glass  or  soapstone,  or 
of  wood  lined  with  metal.  In  the  bottom  of  the  box  is  a  pan  of 
water,  or  a  sponge  kept  constantly  wet.  The  shelves  may  well 
be  of  glass,  and  should  be  so  arranged  that  any  shelf  may  be 
removed  without  disturbing  the  others. 

192.  Water  of  Immersion.  —  When  the  briquets  are  ready  to 
be  immersed,  i.e.,  usually,  twenty-four  hours  after  made,  they  are 
placed  in  a  tank,  containing  water  that  is  kept  fresh  by  frequent 
renewals.     The  water  in  the  tank  should  also  be  maintained  at 
a  nearly  constant  temperature.     It  is  sometimes  the  case  that 
briquets  are  subjected  to  considerable  variations  of  temperature 
while  in  storage.     It  also  frequently  occurs  that  the  water  is 
allowed   to   become   stale.     A   few   of   the   many   experiments 
made  at  St.  Marys  Falls  Canal  to  show  the  effect,  on  the  tensile 
strength  of  natural  cement  briquets,  of  variations  in  the  tem- 
perature of  the  water  of  immersion,  are  given  in  Table  36.     The 
details  of  these  experiments,  as  well  as  other  tests  on  the  same 
point,  may  be  found  in  the  Annual  Report,  Chief  of  Engineers, 
U.  S.  A.,  for  1894,  page  2314. 

The  very  marked  effect  which  the  temperature  of  the  water 
may  have  on  the  rate  of  hardening  of  natural  cements  is  clearly 
shown.  When  broken  at  the  age  of  one  day  or  seven  days, 
the  effect  on  the  strength  may  not  be  evident,  or  the  briquets 
stored  in  cold  water  may  develop  a  greater  strength,  but  the 
more  rapid  hardening  of  the  briquets  stored  in  warm  water  is 
usually  very  evident  at  twenty-eight  days,  and  increases  up  to 
two  or  three  months.  Some  samples  of  cement  are  affected 


120 


CEMENT  AND  CONCRETE 


less  than  others,  and  a  few  experiments  indicated  that  the 
differences  in  strength  due  to  the  temperature  of  water  of  im- 
mersion decrease  after  three  months  and  become  almost  nil  at 
one  year. 

193.  The  conclusion  drawn  from  these  tests  may  be  briefly 
stated  as  follows:  Between  certain  limits  the  early  strength  of 
natural  cement  mortars  is  usually  developed  faster  in  cool 

TABLE    36 

Variations    in    Temperature    of     Water    in    which    Briquets    are 

Immersed 


a 

6 

( 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE 

ft 

NATURAL 

"^  Sr       H 

2 

INCH,  WHEN  IMMERSED  IN 

H 

CEMENT. 

9  Q  E-TtC 

WATER  OF  APPROXIMATE  TEMPERATURE, 

U 

sill 

&  y 

DEGREES  FAHR. 

1 

Brand. 

Sample. 

—  A        — 

oj 

—  O1 

38° 

40° 

50° 

55° 

60° 

65° 

70° 

•80° 

PH 

OH 

j 

Gn 

15  R 

o 

Tdavs 

146 

137 

125 

126 

154 

2 

0 

LIC*^  0 

14  days 

144 

. 

131 

125 

131 

150 

168 

208 

3 

0 

28  days 

166 

.  .  . 

178 

.  .  . 

184 

.  .  . 

247 

280 

4 

1 

7  days 

83 

.  .  . 

88 

84 

89 

98 

97 

121 

5 

1 

14  days 

84 

.  .  . 

111 

123 

.  .  . 

150 

191 

.  6 

1 

28  days 

96 

.  .  . 

156 

187 

.  .  . 

221 

243 

288 

7 

Ln 

31  S 

0 

1  day 

.  . 

143 

.  .  . 

124 

120 

.  .  . 

109 

109 

8 

0 

7  days 

. 

204 

201 

.  . 

183 

.  .  . 

193 

186 

9 

0 

14  days 

. 

184 

203 

.  .  . 

204 

.  •  . 

229 

245 

10 

0 

28  days 

. 

221 

245 

.  .  . 

254 

.  .  . 

281 

303 

11 

0 

2  mos. 

. 

261 

292 

.  .  . 

348 

.  .  . 

382 

429 

12 

An 

G 

1 

7  days 

.  . 

134 

140 

.  .  . 

150 

.  .  . 

154 

158 

13 

1 

14  days 

.  . 

149 

162 

.  .  . 

189 

.  .  . 

182 

216 

14 

1 

28  days 

.  .  . 

198 

223 

250 

.  .  . 

281 

296 

15 

1 

2  mos. 

.  .  . 

251 

286 

337 

386 

403 

16 

3 

14  days 

.  .  . 

50 

58 

.  .  . 

69 

73 

100 

17 

3 

28  days 

.  .  . 

67 

87 

100 

102 

157 

18 

3 

2  inos. 

104 

127 

147 

.  .  . 

194 

231 

water,  but  after  the  first  seven  days,  and  sometimes  after  a 
shorter  time,  the  strength  is  developed  more  rapidly  in  warm 
water,  and  the  strength  at  any  time  between  seven  days  and 
three  months  is  approximately  proportional  to  the  temperature. 
After  three  months,  the  effect  of  the  temperature  seems  to 
diminish,  and  may  entirely  disappear  in  time. 

M.  Paul  Alexandre  l  made  quite  a  number  of  experiments 
on  this  point  with  Portland  cement.     In  these  experiments  the 


"  Recherches  Experimentales  sur  les  Mortiers  Hydrauliques." 


STORING  BRIQUETS  121 

gaging  was  done  in  about  the  same  temperature  as  that  at  which 
the  water  of  immersion  was  maintained,  so  that  a  double  cause 
of  variation  was  present.  However,  it  was  found  that  in  all 
cases  the  higher  strength  was  attained  at  seven  days  by  the 
briquets  made  and  stored  in  the  higher  temperature  (15°  to 
18°  C.,  60°  to  65°  Fahr.)  while  at  twenty-eight  days  the  briquets 
of  the  lower  temperature  (0°  to  5°C.,  32°  to  40°  Fahr.)  were 
ahead  in  the  case  of  neat  cement,  and  nearly  as  high  as  the 
warm  briquets  in  the  case  of  mortar.  At  three  months  the 
differences  seemed  to  disappear. 

194.  Stale  Water.  —  Some  experiments  made  to  compare  the 
strength  of  briquets  which  were  alike  in  all  other  respects,  but 
were  immersed  in  different  tanks  in  which  the  water  had  not 
been  frequently  renewed,  showed  very  clearly  the  possible  varia- 
tions from  this  source.     Natural  cement  briquets,  neat,  and  with 
one  and  two  parts  sand,  gave,  when  immersed  in  one  of  the 
tanks,  only  from  40  to  60  per  cent,  of   the   strength  attained 
in  another  tank  by  briquets  entirely  similar. 

To  store  briquets  in  running  water  is  going  to  the  other 
extreme;  this  appears  to  be  the  best  method,  at  least  for  short- 
time  acceptance  tests,  provided  the  temperature  can  be  regu- 
lated. However,  in  some  cases  where  this  has  been  adopted, 
the  strength  of  the  briquets  is  said  to  have  fallen  off  very  much 
after  four  or  five  years.  Whether  this  is  due  to  the  action  of 
running  water  is  a  very  interesting  point,  and  a  valuable  one 
from  the  practical  standpoint  of  the  use  of  cement,  but  it  has 
not  yet  been  thoroughly  investigated. 

195.  It  appears    from  the  foregoing  that  variations  in  the 
temperature  and  freshness  of  the  water  in  which  the  briquets 
are  immersed  is  an  uncertain  contingent,  and  therefore  that  all 
such  variations  should  be  carefully  avoided.     As  a  matter  of 
convenience,  the  tanks  may  well  be  maintained  at  60°  to  70° 
Fahr.,  but  if  one  does  not  care  for  a  comparison  of  his  results 
with  those  obtained  in  other  laboratories,  then  any  other  con- 
stant temperature  between  40°  and  75°  may  be  adopted.     The 
water  in  the  tanks  should  be  renewed  at  least  once  a  month, 
and  preferably  once  a  week. 

196.  Storing   Briquets   in   Sea  Water.  —  When    the    cement 
under  test  is  to  be  usod  for  constructions  in  the  sea,  some  of 
the  briquets  should  be  stored  in  sea  water  to  indicate  the  be- 


122  CEMENT  AND   CONCRETE 

havior  in  this  medium.  Many  tests  have  been  made  in  this 
way  by  several  experimenters,  but  the  varied  results  obtained 
only  indicate  the  different  effects  of  such  treatment  on  different 
samples  of  cement.  One  of  the  effects  of  storing  in  sea  water 
has  been  touched  upon  under  the  head  of  consistency  of  mortar, 
where  it  is  shown  that  porous  briquets  may  disintegrate  in  this 
medium.  A  small  specimen  like  a  briquet  will  of  course  be 
more  quickly  affected  than  a  large  mass  of  concrete,  but  on  the 
other  hand,  the  concrete  in  work  is  likely  to  be  more  porous 
than  the  briquet.  The  effect  of  sea  water  upon  cement  will  be 
taken  up  in  another  place. 

197.  Other  Methods  of  Storing  Briquets.  —  It  has  been 
thought  that  briquets,  made  to  test  cement  that  is  to  be  used 
in  air,  should  be  hardened  in  the  same  medium  in  order  that 
the  tests  should  more  nearly  approach  the  conditions  of  use. 
Several  points,  however,  should  be  borne  in  mind  in  interpret- 
ing the  results  obtained  with  air-hardened  specimens.  In  actual 
work  the  mortar  is  usually  in  a  large  mass,  or  is  protected  from 
the  influence  of  a  warm,  dry  atmosphere,  so  that  it  remains 
moist  for  a  long  time,  whereas  a  briquet  placed  in  the  open 
air  is  much  more  affected  by  changes  in  atmospheric  condi- 
tions. If  the  briquets  are  allowed  to  harden  in  a  room,  such  a 
small  quantity  of  mortar  may  become  quite  dry  in  a  few  days, 
and,  unless  the  amount  of  moisture  in  the  air  is  regulated,  an- 
other source  of  variation  is  introduced  in  the  tests. 

It  has  been  found  impossible  to  obtain  uniform  results  from 
briquets  made  as  nearly  alike  as  possible  and  stored  side  by 
side  in  the  air  of  the  laboratory.  The  regular  acceptance  tests 
should,  therefore,  it  is  thought,  be  made  in  the  ordinary  man- 
ner, but  if  cement  is  to  be  used  in  locations  where  it  is  likely 
to  become  very  dry,  a  few  special  tests  should  be  made  to  assure 
one  that  the  brand  of  cement  in  question  is  one  that  will  yield 
good  results  in  such  exposure.  It  may  be  found  that  certain 
kinds  or  brands  should  be  entirely  avoided  for  use  in  such  lo- 
cations. A  few  tests  of  this  character  are  given  in  Tables  72 
and  73,  §§  359,  360.  The  results  in  any  given  line  of  the  table 
are  from  briquets  made  the  same  way  but  treated  differently 
in  the  method  of  storing.  It  is  seen  that  these  brands  harden 
well  in  dry  air.  The  effect  of  the  amount  of  water  used  in 
gaging  appears  to  follow  somewhat  the  same  law,  whether  the 
briquets  are  stored  in  air  or  water, 


BREAKING   THE  BRIQUETS  123 

A  method  more  nearly  approaching  conditions  that  fre- 
quently prevail  in  practice  is  to  bury  the  briquets  in  damp 
sand.  Table  120,  §409,  gives  the  results  obtained  with  a  large 
number  of  briquets  stored  in  this  way.  While  the  results  are 
somewhat  more  irregular  than  those  for  water-hardened  speci- 
mens, since  the  conditions  cannot  be  made  so  nearly  uniform, 
yet  this  method  gives  better  results  than  dry  air  storage. 

ART.  25.     BREAKING  THE  BRIQUETS 

198.  THE  TESTING  MACHINE.  —  The  function  of  the  testing 
machine  is  simply  to  furnish  a  means  of  applying  the  tensile 
stress,  and  of  measuring  the  amount  of  force  required  to  break 
the   briquet.     Aside   from   the   clips,   which   hold   the   briquet, 
any    contrivance    which    may    be    conveniently    operated,    and 
which  will  accurately  measure  the  force  applied,  may  be  used 
for  this  purpose. 

There  are  several  forms  of  testing  machines  on  the  market, 
all  designed  on  the  lever  principle,  though  differing  slightly  in 
the  method  of  application.  The  force  is  applied  either  by  al- 
lowing water  or  shot  to  run  into  or  out  of  a  vessel  suspended 
at  the  end  of  the  longer  arm  of  a  lever,  or  a  weight  is  made  to 
run  along  the  lever  arm,  which  is  graduated  so  that  the  force 
applied  may  be  read  from  the  beam. 

199.  In  machines  of   the  first  class  the  delivery  of  shot  is 
cut  off  automatically  the  instant  the  briquet  breaks.     The  ad- 
vantage of  this  style  is  that  the  flow  of  shot  may  be  so  adjusted 
as  to  approximately  regulate  the  rate  of  applying  the  stress; 
but  little  skill  is  required  to  operate  it,  and,  since  in  its  best 
form  two  levers  are  used,  the  shorter  arm  of  one  acting  on  the 
longer  arm  of  the  other,  the  machine  occupies  but  little  space. 
This  machine  does  not  permit  rapid  operation,  since  the  shot 
must  be  weighed  ea.3h  time  a  briquet  is  broken.     One  of  the 
main  disadvantages  of  this  form  has  been  that  in  the  case  of 
strong  briquets,  a  certain  initial  strain  had  to  be  applied  in 
order  that  the  stretch  of  the  briquet  and  the  slipping  of  the 
clips  should  not  allow  the  shot  to  be  cut  off  before  the  briquet 
broke.     This  objection,  however,  has  recently  been  met  by  the 
makers,  who  have  provided  means  of  taking  up  this  slip  by  a 
hand  crank. 

200.  Another   objection  urged   against  the  short-lever  shot 


124  CEMENT  AND  CONCRETE 

machines  is  the  fact  that  as  the  stream  of  shot  flowing  into  the 
scale  pan  is  cut  off  by  the  breaking  of  the  briquet,  a  certain 
amount  of  shot  on  its  way  to  the  pan  falls  into  the  pan  after 
the  briquet  breaks,  and  is  weighed,  although  not  acting  on  the 
briquet  at  the  time  of  the  break.  A  form  of  shot  machine  is 
now  on  the  market,  however,  in  which  this  objection  has  been 
overcome.  The  load  is  applied  by  means  of  a  weight  hanging 
from  one  end  of  a  lever.  This  weight  is  at  first  counterbalanced 
by  a  pail  of  shot  at  the  other  end  of  the  lever,  but  as  the  shot 
is  allowed  to  run  out  of  the  vessel,  the  unbalanced  portion  of 
the  weight  acts,  through  suitable  levers,  upon  the  briquet. 
The  flow  of  shot  is  shut  off  automatically  by  the  breaking  of 
the  briquet,  and  the  shot  that  has  escaped  is  weighed  on  a 
spacial  scale  to  determine  the  load  acting  on  -the  briquet. 

201.  In  the  other  form  of   machine  the  weight   is  made  to 
move  along  the  arm  by  means  of  a  cord  and  hand-wheel.     This 
style  may  be  operated  much  more  rapidly,  but  some  skill  is 
required  to  use  it  properly,  and  as  now  made  it  occupies  too 
much  space.     These  machines  are  preferable  for  laboratories, 
while  the  shot  machines  may  well  be  used  in  cement  factories 
and  small  works  where  a  foreman  does  the  testing. 

202.  It  would   seem  that  a  machine  could  easily  be  made 
which  would  combine  the  desirable  features  of  both  of  these 
forms,  by  placing  a  heavy  weight  provided  with  rollers  upon 
the  upper  lever  arm  of  the  shot  machine,  and  using  it  in  the 
same  way  that  the  hand  power  machine  is  now  used.     This 
would  involve  placing  a  hand  wheel  and  cord  upon  the  machine 
to  operate  the  moving  weight,  the  shot  attachment  being  re- 
moved.    Such  a  machine  would  combine  the  compactness  of 
the  shot  machine,  with  the  accuracy  and  speed  of  the  single 
lever  machine;  the  graduations  on  the  beam  could  represent 
five  pounds  each,  instead  of  two  pounds,  the  value  of  the  grad- 
uations now  on  the  single  lever  machines. 

203.  FORMS  OF  CLIP.  —  Since   cement  has  been  tested  by 
tensile  strain,  it  has  ever  been  a  problem  to  obtain  a  clip  which 
would  give  a  perfectly  true  axial  pull  on  the  briquet.     Various 
forms  of  clips  have  been  used  from  time  to  time,  but  none  of 
them  has  proved  satisfactory  in  all  respects.     To  trace  the  his- 
tory of  the  development  of  the  clip  is  not  warranted  by  its 
interest,  but.it  may  be  said  that  in  some  of  the  early  forms  the 


BREAKING   THE   BRIQUETS 


125 


head  of  the  briquet  was  held  between  two  plates  and  clamped 
tight  enough  to  develop  sufficient  friction  to  transmit  the  stress. 
The  later  forms  of  briquets  are  made  with  a  shoulder  or  with 
wedge-shaped  ends  to  allow  the  clip  to  grasp  them.  Mr.  John 
Grant,  Mr.  Alfred  Noble,  General  Gilmore,  Mr.  J.  Sondericker 
and  Mr.  D.  J.  Whittemore  have  each  designed  or  adapted  dif- 
ferent forms,  and  more  recently  Mr.  S.  Bent  Russell  and  Mr. 


I"  **   H    *    0  I  Z  3//T. 

FlO.  6.  — RIEHLE  "ENGINEERS'   STANDARD"   CLIP 

W.  R.  Cock  have  each  devised  a  clip  which  will  be  mentioned 
below. 

204.  Form  in  Most  General  Use.  —  The  clip  in  most  general 
use  in  the  United  States  is  of  the  general  style  shown  in  Fig.  6. 
It  differs  only  in  detail  from  the  form  recommended  by  the 
Amer.  Soc.  C.  E.  Committee  of  1885,  which  has  been  called 


126  CEMENT  AND  CONCRETE 

the  "Engineers'  Standard.".  The  general  form  is  pear  shaped; 
the  briquet  is  grasped  at  the  points  of  reverse  curve  at  the  side 
of  the  briquet,  giving  an  area  between  opposite  gripping  points 
of  about  one  and  a  quarter  square  inches.  The  gripping  points 
are  rather  too  sharp,  when  new,  as  they  have  a  tendency  to 
crush  the  briquet  locally.  The  width  of  the  bearing  increases 
with  the  amount  of  wear  the  clip  sustains.  The  clip  is  provided 
with  a  conical  pivot,  which  rests  in  a  cone-shaped  cavity  at- 
tached to  the  machine,  so  that  the  two  parts  of  the  clip  are 
free  to  swing.  In  a  form  which  was  previously  used  to  a  con- 
siderable extent,  each  bearing  surface  was  designed  to  be  about 
an  inch  square,  the  jaw  being  made  to  conform  to  the  outline 
of  the  briquet.  This  form,  however,  did  not  give  satisfactory 
results;  a  particle  of  sand  between  the  briquet  and  the  bearing 
surface  of  the  clip  would  give  an  eccentric  pull,  and  strong 
briquets,  would  sometimes  break  in  the  head  of  the  briquet 
transverse  to  the  axis,  in  several  curved  layers  joining  opposite 
gripping  surfaces. 

205.  CLIP-BREAKS.  —  When  a  briquet  is  inserted  in  the  or- 
dinary clip,  the  gripping  points  will  not,  in  general,  grasp  the 
briquet  symmetrically.     The  gripping  points  have  a  tendency 
to  slide  on  the  surface  of  the  briquet  in  order  to  assume  a  sym- 
metrical position;  there  is  friction  to   resist  this  sliding,   and 
when  this  resistance  overcomes  the  tendency  to  motion,  the  two 
clips  and  the  briquet  become  a  rigid  system,  and  bending  strains 
may  be  introduced.     Again,  if  the  briquet  is  not  too  badly  ad- 
justed in  the  clips,  it  is  apt  to  break  in  a  line  joining  two  op- 
posite gripping  points,  instead  of  at  the  smallest  section;  this 
is  called  a  "  clip-break."     The  tendency  to  form  clip-breaks  is 
greater  if  the  gripping  points  are  very  narrow  or  have  sharp 
edges;  neat  cement  briquets  exhibit  this  tendency  much  more 
than  briquets  from  sand  mortars,  and  some  samples  of  cement 
are  much  more  likely  to  give  clip-breaks  than  others. 

206.  Cause  of  Clip-breaks.  —  When  a  briquet  breaks  in  this 
manner,  the  broken  section  is  usually  about  normal  to  the  side 
of  the  briquet  at  the  point  where  the  jaw  was  in  contact.     This 
indicates  that  a  clip-break  is   caused  by  compression  at  that 
place:  there  is  evidently  compression  along  the  plane  joining 
the  two  opposite  gripping  points,  and  tension  at  right  angles 
to  that  plane,  and  the  briquet  fails  here  as  a  result  of  the  two 


BREAKING   THE  BRIQUETS  127 

stresses.  If  the  briquet  is  not  properly  adjusted  in.  the  clips, 
but  is  so  placed  that  its  longest  axis  is  at  one  side  of  the  line 
joining  the  points  of  application  of  the  forces  (in  the  "  Engi- 
neers' Standard"  clip,  the  line  joining  the  pivot  points),  then 
the  bending  strain  that  is  introduced  is  greatest  at  the  central 
section  of  the  briquet;  this  may  cause  the  briquet  to  break  at 
the  smallest  section,  when  if  it  were  properly  adjusted  in  the 
clips  it  would  develop  a  clip-break.  The  bearing  surfaces  of 
the  clip  should  not  be  too  small,  as  this  increases  the  intensity 
of  pressure,  but  on  the  other  hand  there  appears  to  be  no  prac- 
tical advantage  in  making  this  area  more  than  j\  to  £  inch 
wide  (the  length  being  limited  by  the  thickness  of  the  briquet, 
one  inch). 

207.  Prevention    of    Clip-breaks. -- The    method    most    fre- 
quently adopted  to  prevent  clip-breaks  is  to  cushion  the  grip- 
ping points  with  some  compressible  material,  such  as  thin  rub- 
ber or  blotting-paper.     This  device   prevents   clip-breaks,   but 
the  result  of  about  three  hundred  tests  made  under  the  author's 
direction   showed    clearly    that    it    also    lowered    the    apparent 
strength  very  materially.1     Briquets  broken  with  the  bare  clips 
showed  a  mean  strength  of  606  pounds  per  square  inch,  while 
the  cushioned  clips  gave  an  apparent  strength  of  but  521  pounds, 
or  86  per  cent,  of  the  strength  without  the  cushion;  of  the  bri- 
quets broken  with  the  bare  clips,  33  per  cent,  were  clip-breaks; 
with  the  cushioned  clips  no  clip-breaks  occurred.     The  rubber 
was  applied  by  slipping  two  rubber  bands  over  each  end  of  the 
briquet,  giving  cushions  about  TV  inch  thick. 

208.  Strength  of  Briquets  that  Develop  Clip-breaks.  —  It  was 
also  found  in  breaking  277  briquets  with  two  styles  of  clips 
without  cushions  that  129  of  them  that  gave  clip-breaks  aver- 
aged 611  pounds  per  square  inch,  while  148  which  did  not  de- 
velop clip-breaks  had  a  mean  strength  of  590  pounds.     This 
result  is  easily  accounted  for  by  saying  that  some  of  the  bri- 
quets that  broke  in  the  small  section  were  made  to  do  so  by  the 
cross-strain  introduced  by  imperfect  adjustment  in  the  clips. 

When  a  briquet  breaks  at  other  than  the  smallest  section,  it 
is  certain  that  the  smallest  section  has  a  greater  strength  per 

1  For  a  report  of  these  tests  in  detail,  see  Annual  Report  Chief  of  Engi- 
neer's, U.  S.  A.,  1895,  p.  2913.  Also  "Municipal  Engineering;1  Dec.,  1896, 
Jan.,  Feb.,  1897. 


128 


CEMENT  AND  CONCRETE 


square  inch  than  is  shown  by  the  result  obtained ;  how  much 
greater  cannot  be  told.  But  it  follows  that  if  clip-breaks  could 
be  eliminated  in  a  proper  way,  one  which  would  not  cause  center 
breaks  by  the  introduction  of  cross-strains  or  other  undesirable 
conditions,  the  strengths  thus  obtained  would  be  greater  than 
when  clip-breaks  occur.  -The  fact  that  the  use  of  a  rubber 
cushion  gives  lower  strengths,  shows  that  this  is  not  the  proper 
method  of  preventing  clip-breaks. 

209.   Mr.  W.  R.  Cock  has  devised  a  clip,  with  rubber-covered 
gripping  points,  which  has  attracted  some  attention.     It  has 


f  Vt  £  ft   0  I  2 

FIG.  7.— RUSSELL  CLIP 

sometimes  been  assumed  that  because  this  clip  eliminated  clip- 
breaks  it  must  give  a  higher  apparent  strength  than  the  rigid 
form.  No  extensive  series  of  experiments  have  been  published 
which  permit  of  comparing  this  clip  with  other  forms,  but 
from  the  results  obtained  above,  in  using  rubber  cushions,  it 
would  appear  that  the  Cock  clip  may  give  lower  apparent 
strengths. 


BREAKING   THE  BRIQUETS 


129 


210.  The  form  of  clip  designed  by  Mr.  S.  Bent  Russell  is 
constructed  on  the  "evener"  principle,  each  clip  having  free- 
dom of  motion  imparted  by  four  pin-connected  joints  (see  Fig. 
7).  It  is  sought  to  prevent  any  but  an  axial  pull  being  ap- 
plied to  the  briquet.  On  account  of  details  of  construction, 
into  which  it  is  not  necessary  to  enter  here,  the  clip  must  be 
in  its  normal  position  when  the  briquet  is  inserted,  in  order 
that  the  possibility  of  cross-strain  shall  be  effectually  removed. 
As  a  result  of  many  tests  with  this  form  and  the  ordinary  "En- 


it  o  a 

FlO.  8.  — SINGLE  GIMBAL  CLIP 


3  in. 


gineers'  Standard,"  it  was  found  that  they  gave  very  nearly 
the  same  strength.  But  that  the  evener  motion  itself  was  of 
some  value  was  shown  by  a  series  of  experiments  in  which  part 
of  the  briquets  were  broken  by  this  form  of  clip  without  modi- 
fication, while  part  were  broken  by  the  same  clip  when  it  had 
been  changed  to  a  rigid  form  by  means  of  a  clamp  that  elimi- 
nated the  evener  motion.  It  is  believed  that  with  some  modifi- 
cations this  clip  will  give  good  results,  and  it  may  be  used  al- 
most as  rapidly  as  the  ordinary  rigid  form. 


130  CEMENT  AND  CONCRETE 

211.  Several  experiments  were  made  with  a  clip    in  which 
the  gimbal  principle  was  applied,  the  stress  passing  from  the 
machine  to  the  gripping  points  through  knife  edges  placed  in 
the  line  joining  opposite  gripping  points  and  midway  between 
them1  (Fig.  8).     Higher  results  were  obtained  with  this  form, 
the  "  Single  Gimbal,"  than  with  any  of  the  styles  with  which  it 
was  compared,  but  it  was  made  only  for  experimental  purposes, 
and   unless   modified  is   not   convenient  enough  to   be   recom- 
mended for  general  use. 

212.  In  the  course  of  these  experiments  it  was  shown  that  to 
increase  the  distance  between  gripping  points,  grasping  the  bri- 
quet  nearer    the    head,  increased    the    apparent    strength    and 
diminished  the  number  of  clip-breaks.     With  the  Russall  clip, 
increasing  this  distance  from  l^V  inches  to  !T7g-  inches  gave  an 
increase  of  about  six  per  cent,  in  the  apparent  strength;  and  a 
similar  increase  in  the  width  between  jaws  of  the  Gimbal  clip, 
from  lf\  to  1-&  inches,  gave  an  increase  in  apparent  strength 
of   about  five  per  cent.      It  was  found  later  that  Mr.  J.  Son- 
dericker  had  previously  arrived  at  similar  results,2  and  as  the 
form  of  briquet  used  by  the  latter  had  permitted  extending 
the  experiment,  he  found  that  when  the  points  were  about  If 
inches  apart  (making  the  area  of  the  briquet  about  If  square 
inches  between  opposite  gripping  points),  nearly  all  the  frac- 
tures occurred  at  the  smallest  section. 

213.  Effect   of   Improper  Adjustment.  —  The   effect    of   not 
properly  adjusting  the  briquets  in  the  clip  was  also  investigated. 
In  some  cases  the  briquets  were  placed  in  the  proper  position 
as  nearly  as  possible.     In  the  other  cases  they  were  in  a  de- 
cidedly  distorted   position,    much   worse   than   they   would   be 
placed  with  the  most  careless  manipulation.     It  was  found  that 
if   the   briquet   was   so   placed   in   the   " Engineers'    Standard" 
clip  that  the  gripping  points  on  one  side  of  the  briquet  were 
farther  apart  than  those  on  the  other  side,  the  decrease  in  break- 
ing strength  was  very  marked  (about  35  per  cent.),  while  if  the 
planes  determined  by  the  lines  of  contact  of  the  gripping  points 
of  each  clip  were  parallel,  there  appeared  to  be  no  effect.     The 


1  This  clip  was  devised  by  the  author  at  the  suggestion  of  Mr.  E.  S. 
Wheeler,  M.  Am.  Soc.  C.  E. 

2  Jour.  Assoc.  Eng.  Soc.,  Vol.  vii,  p.  212. 


BREAKING   THE  BRIQUETS  131 

reason  of  this  is  evident:  in  the  former  case  the  line  of  force, 
joining  the  two  pivot  points,  does  not  pass  through  the  center 
of  the  smallest  section  of  the  briquet,  and  transverse  stresses 
are  introduced,  while  in  the  latter  case  the  line  of  force  does 
pass  through  the  center  of  the  smallest  section,  though  not  at 
right  angles  to  its  plane.  With  the  Russell  and  Gimbal  clips 
the  distortion  seemed  to  have  little  effect,  provided,  that  in 
the  case  of  the  former,  the  clip  was  itself  in  its  normal  position 
when  the  briquet  was  inserted. 

214.  Conclusions  Derived  from  Tests  of  Several  Styles  of 
Clips.  —  From  the  tests  described  above,1  the  following  conclu- 
sions may  be  drawn:  - 

1st.  When  using  the  ordinary  form  of  clips  with  metal 
gripping  points,  the  briquets  which  break  at  the  places  of  con- 
tact of  the  jaws  give  higher  apparent  strengths  than  those 
which  break  at  the  smaller  sections. 

2d.  A  rubber  cushion  between  the  briquet  and  the  jaw  of 
the  clip  prevents  clip-breaks,  but  materially  lowers  the  stress 
required  to  break  the  briquet. 

3d.  The  form  of  clip  designed  by  Mr.  S.  Bent  Russell  gives 
somewhat  less  irregular  results  than  are  obtained  with  the 
Riehle  " Engineers'  Standard"  rigid  clip.  Although  the  results 
given  by  the  Russell  clip  in  its  present  form  are  a  trifle  lower 
than  those  given  by  the  Riehle,  it  seems  probable  that  these 
lower  results  are  due  to  defects  in  detail  which  may  readily 
be  eliminated. 

4th.  By  the  application  of  the  gimbal  principle  to  cement 
testing  clips,  higher,  as  well  as  more  nearly  uniform,  results 
may  be  obtained. 

5th.  In  using  the  rigid  form  of  clip,  careless  manipulation 
in  adjusting  the  briquet  may  result  in  serious  error  due  to  the 
introduction  of  cross-strains,  while  with  either  the  Single  Gim- 
bal or  Russell  clip  slight  deviations  in  adjustment  are  not  im- 
portant. 

6th.  With  the  form  of  briquet  recommended  by  the  commit- 
tee of  the  American  Society  of  Civil  Engineers  in  1885,  the  break- 
ing stress  may  be  somewhat  increased,  and  the  number  of  clip- 


1  These  tests  were  described  in  greater   detail  and    discussed    by  the 
writer  in  "Municipal  Engineering,"  Dec.,  1896,  Jan.  and  Feb.,  1897. 


132 


CEMENT  AND  CONCRETE 


breaks  may  be  very  materially  decreased,  by  such  a  modifica- 
tion of  the  clip  as  to  allow  grasping  the  briquet  nearer  the  head. 

215.  Requirements  for  a  Perfect  Clip.  —  As  a  logical  result 
of  these  conclusions,  the  ideal  clip  should  fulfill  the  following 
requirements :  — 

1st.  It  should  impart  a  true  axial  pull  to  the  briquet  with- 
out subjecting  it  either  to  cross-strains  or  to  compressive  forces 


liilnl 


r  »A  YL  ft  o  i  2 

FlG.  9.  — FORM  OF  ARTICULATED  CLIP  SUGGESTED   FOR  USE 

sufficient  to  cause  it  to  break  at  other  than  the  smallest  section. 
2d.  The  bearing  surfaces  of  the  gripping  points  should  not 
be  more  than  about  one-fourth  of  an  inch  wide,  since  this  is 
sufficient  to  prevent  crushing  the  briquet  at  these  places,  and 
too  wide  a  jaw  will  not  usually  bear  uniformly  over  its  whole 
surface. 


BREAKING  THE  BRIQUETS 


133 


3d.  Its  parts  should  have  sufficient  strength  and  stiffness, 
so  that  they  will  not  bend  appreciably  when  in  use. 

4th.    It  should  permit  rapid  operations,  and 

5th.  It  should  be  as  light  as  consistent  with  the  above 
requirements. 

216.  Form  Suggested.  —  Fig.  9  shows  a  style    of  clip  which 
closely    conforms    to    the   above     specifications.       The   evener 
form  devised  by  Mr.  Russell  has  been  selected  for  modification. 
The  S.  G.  clip  would  more  nearly  meet  some  of  the  requirements, 
and,  so  far  as  the  principle  is  concerned,  this  form  is  considered 
quite  the  equal  of  the  evener  clip.     But  no  method  of  applying 
the  gimbal  principle  has   commended  itself  as  affording  such 
rapid  manipulation  as  does  the  evener  motion,  and  since  it  is 
thought  that  either  form  will  obviate  cross-strains  in  a  plane 
parallel  to  the  face  of  the  briquet,  the  evener  form  has  been 
adopted  on  account  of  convenience. 

The  defeats  in  detail  of  the  Russell  clip  which  have  already 
been  mentioned  have  been  obviated  in  the  present  form.  The 
gripping  points  are  made  one-fourth  of  an  inch  wide,  and  a  little 
more  material  has  been  used  between  the  gripping  points  and 
the  first  pin  to  stiffen  the  clip.  This  form  is  designed  for  use 
with  the  briquet  shown  in  Fig.  5  (see  §  179). 

217.  RATE  OF  APPLYING  THE  TENSILE  STRESS.  —  Table  37 
gives  the  results  of  several  hundred  experiments  made  by  Mr. 

TABLE  37 
Relation  of  Apparent  Tensile  Strength  to  Rate  of  Applying  Stress 


RATE  OF  APPLYING 

TENSILE  STRENGTH 

STRESS, 
POUNDS  PER  MINUTE. 

OBTAINED, 
POUNDS  PER  So,.  INCH. 

50 

400 

100 

415 

200 

430 

400 

450 

6,000 

493 

Henry  Faija  *  to  show  the  effect  on  tensile  strength  of  varying 
the  rate  of  applying  the  stress. 

A  few  of  the  results  obtained  from  nearly  900  tests,  made 

1  "Cement  for  Users,"  by  Mr.  Henry  Faija. 


134 


CEMENT  AND  CONCRETE 


under  the  author's  direction  to  illustrate  this  point,  are  given 
in  Table  38.  Some  of  these  results  accord  very  well  with  those 
given  in  Table  37,  but  the  results  in  the  latter  table  were  doubt- 
less obtained  from  neat  Portland  briquets  only,  while  the  ex- 
periments given  in  Table  38  were  made  with  briquets  neat 
and  with  two  parts  sand,  and  on  natural  as  well  as  Portland 
cement  mortars. 

TABLE   38 

Relation  of  Apparent  Tensile  Strength  to  the  Rate  of  Applying  the 

Stress 


TENSILE  STRENGTH,  POUNDS  PER 

SQUARE  INCH,  FOR  STRESS  APPLIED  AT 

CEMENT. 

PROPORTIONS. 

AOK    OF 

BRIQUETS. 

RATE  OF  POUNDS  PER  MINUTE. 

100 

300 

500 

700 

900 

Portland 

Neat  cement 

7  and  14  days 

453 

485 

521 

520 

528 

it 

Neat  cement 

3  months 

•  •  • 

590 

617 

622 

640 

n 

1-2 

3  months 

445 

467 

487 

507 

510 

Natural 

Neat  cement 

7  days 

150 

169 

186 

.  .  . 

202 

K 

Neat  cement 

3  months 

309 

351 

363 

378 

390 

U 

1-2 

3  months 

255 

299 

327 

329 

354 

218.  It  appears  from  all  these  results  that  the  increase  in 
the  breaking  strength  due  to  increasing  the  rate  of  applying 
the  stress  is  considerable  in  the  case  of  low  rates  of  speed,  but 
when  a  rate  of  500  or  600  pounds  per  minute  has  been  reached, 
a  further  increase  in  rapidity  does  not  make  a  material  increase 
in  the  apparent  strength.     Since  certain  variations  in  rate  are 
sure  to  occur,  until  some  device  is  used  to  automatically  regu- 
late it,  a  rate  should  be  adopted  which  would  allow  of  slight 
variations  without  materially  changing  the  result  of  the  test. 
A  rate  of  600  pounds  per  minute  would  fulfill  this  requirement, 
and,  with  certain  machines  at  least,  would  be  still  more  con- 
venient than  the  rate  of  400  pounds  per  minute  which  has  here- 
tofore been  quite  generally  used. 

An  analysis  of  the  -experiments  made  to  determine  the  de- 
gree of  uniformity  obtained  by  using  each  of  the  given  rates, 
showed  there  was  but  little  difference  in  this  regard,  but  if 
any  choice  could  be  made  on  this  basis  it  seemed  to  lie  with 
the  more  rapid  rate. 

219.  With  the  shot  machines  it  is  not  difficult  to  approxi- 


BREAKING   THE  BRIQUETS  135 

mately  regulate  the  rate  at  which  the  stress  is  applied.  In 
operating  a  machine  in  which  a  handwheel  moves  a  weight 
along  the  graduated  beam,  it  must  be  remembered  that  the  rate 
at  which  the  weight  moves  is  the  controlling  factor,  and  not 
the  movement  of  the  lower  wheel,  which  simply  serves  to  take 
up  lost  motion,  the  stretch  of  the  briquet  under  strain,  and 
the  slipping  of  the  briquet  in  the  jaws  of  the  clip.  A  mistaken 
idea  concerning  this  matter  has  sometimes  led  to  the  adoption 
of  a  device  to  regulate  the  motion  of  this  lower  wheel.  Until 
one  is  accustomed  to  applying  the  stress  at  a  given  uniform 
rate,  he  will  find  it  an  aid  to  hang  near  the  machine  a  pendulum 
of  such  a  length  that  a  certain  number  of  vibrations  correspond 
to  a  complete  revolution  of  the  handwheel. 

220.  Treatment  of  the  Results.  —  The   number  of   briquets 
which  are  made  to  test  the  strength  of  a  given  sample  of  cement 
will  depend  on  the  accuracy  which  it  is  desired  to  attain.     If 
but  two  briquets  are  made,  neither  of  the  results  may  be  re- 
jected; however  widely  they   may   differ  one  from   the  other, 
the  mean  of  the  two  must  be  considered  the  result  of  the  experi- 
ment when  nothing  is  known  as  to  their  comparative  value. 
But  if  several  briquets  are  made  from  the  same  sample,  and 
they  vary  one  from  another,  the  final  result  is  sometimes  ob- 
tained by  rejecting  certain  of  the  observations.     In  some  cases 
if  five  or  six  specimens  are  made,  the  highest  and  the  lowest 
ones  are  omitted,  while  sometimes  the  two  lowest  are  rejected, 
and  the  mean  of  the  three  or  four  highest  is  taken. 

221.  While  the  absolute  mean  of  all  of  the  observations  will 
ordinarily  be  quite  sufficient,  and  should  usually  be  considered 
the  result  of  the  test,  yet  where  tests  are  very  carefully  made 
to  compare  two  samples,  or  two  methods  of  manipulation,  it 
may  be  desired  to  reject  certain  observations  that  appear  to 
be  abnormal.     The  beginner  in  cement  testing,  unfamiliar  with 
observations  of  this  character,  may  not  feel  confidence  in  his 
own  judgment  as  to  what  observations  may  be  rejected,  and  the 
criteria  sometimes  used  in  more  accurate  work  are  entirely  too 
complicated   for   this   purpose.     To   serve   as   a   guide  in  such 
cases,   the   writer  would  suggest  the  following  simple  method 
which,  though  entirely  arbitrary,  is  more  justifiable  than  either 
of  the  methods   mentioned  above.     As   the  experimenter  be- 
comes more  familiar  with  the  work,  he  will  doubtless  prefer  to 


13G 


CEMENT  AND  CONCRETE 


depend  on  his  own  judgment  in  the  rejection  of  observations, 
taking  into  account  the  general  accuracy  of  the  work. 

First  obtain  the  absolute  mean  and  the  difference  between 
this  mean  and  each  individual  result;  let  us  call  this  difference 
the  "error"  for  each  result.  Reject  any  observations  whose 
error  is,  say,  ten  per  cent,  of  the  absolute  mean,  and  obtain  the 
mean  of  the  remaining  observations  as  the  true  result. 

222.  For  example,  suppose  that  we  have  broken  ten  bri- 
quets obtaining  the  strengths  given  below,  and  wish  to  deter- 
mine the  result  of  the  test.  The  absolute  mean  is  found  to  be 
213.9  pounds,  or,  the  nearest  whole  number,  214  pounds. 

TABLE   39 
Rejection  of  Observations 


NUMBER 

OF 

BRIQUETS. 

OBSERVED 
STRENGTH. 

ERROR. 

OBSERVED 
STRENGTH. 

NEW 
ERROR. 

1 

209 

5 

209 

1 

2 

226 

12 

226 

16 

3 

227 

13 

227 

17 

4 

184 

30 

5 

217 

3 

217 

7 

6 

252 

38 

7 

200 

14 

200 

10 

8 

195 

19 

195 

15 

9 

193 

21 

193 

17 

10 

236 

22 

.  .  . 

Sum  . 

2,139 

177 

1,467 

83 

Mean      .     . 

213.9 

17.7 

209.6 

11.9 

The  " errors"  are  given  in  the  third  column,  and  it  is  seen 
that  three  of  them  are  greater  than  ten  per  cent,  of  the  mean. 
Omitting  the  results  having  these  large  errors,  we  obtain  a  new 
mean  of  209.6  pounds,  which  is  to  be  considered  the  result  of 
the  test.  An  inspection  of  the  first  column  of  errors  shows  that 
the  mean  of  the  errors  is  17.7  pounds;  if  we  divide  this  by  the 
mean  of  the  tensile  strengths,  we  obtain  17.7  •*•  213.9  =  .0827. 
Expressing  this  as  a  percentage,  we  may  call  8.27  per  cent, 
the  "  average  error."  The  same  result  is,  of  course,  obtained 
by  dividing  the  sum  of  errors  by  the  sum  of  the  strengths. 
Now  if  we  consider  column  five,  we  see  that  the  new  average 
error  will  be  but  83  -*-  1467  =  5.66  per  cent. 


I       INTERPRETATION  137 

223.  In  giving  the  results  of  a  series  of  tests,  it  is  a  common 
practice  to  state  only  the  absolute  mean,  but  it  is  of  considerable 
interest  to  know  the  variations  that  occurred  in  breaking  in 
order  that  one  may  judge  of  the  reliability  of  the  results,  or, 
in  other  words,  to  make  a  rough  approximation  as  to  the  prob- 
able error.     For  this  purpose  the  highest  and  lowest  result  may 
be  given,  but  a  much  better  index  to  reliability  would  be  tc 
give   the   " average   error"    as   explained   above.     However,   in 
reporting  a  large  number  of  tests,  the  extra  labor  involved  in 
obtaining  this  " average  error"  is  usually  considered  too  great 
to  be  attempted,  and  in  such  cases  the  absolute  mean  and  the 
highest  and  lowest  results  must  serve  the  purpose. 

224.  Accuracy  Obtainable.  —  When  an  operator  has  become 
expert  and  is  working  under  good  conditions,  he  may  expect 
to  obtain  results  within  the  following  limits:  The  extreme  varia- 
tions between  the  results  in  a  set  of  ten  briquets  (the  difference 
between  the  highest  and  lowest)  not  exceeding  20  per  cent,  of 
the  mean  strength  of  the  set,  the  maximum  variation  from  the 
mean  not  exceeding  12  per  cent,  of  the  mean,  and  the  " aver- 
age error,"  as  explained  above,  not  exceeding  8  per  cent. 

ART.  26.     THE  INTERPRETATION  OF  TENSILE  TESTS  OF 
COHESION 

225.  One  of   the  problems   presented  in  the  inspection  of 
cement  is   to  foretell   the   ultimate   relative  strengths   of  two 
samples  from  the  results  of  short  time  tests.     Formulas  have 
been  presented  purporting  to  solve  this  problem,  such  formulas 
being  based  on  the  assumption  that  the  strength  gained  at  the 
end  of  months  or  years  is  a  function  of  that  developed  in  a  few 
days.     In  fact,  the  raison  d'etre  of  tensile  or  other  short-time 
strength  tests  for  the  acceptance  of  cement,  rests,  in  a  sense, 
upon  this  same  assumption. 

The  value  of  strength  tests  as  one  of  the  guides  in  determin- 
ing in  a  short  time  the  probable  quality  of  a  cement  is  unques- 
tioned. One  is  apt,  however,  to  seek  too  close  an  agreement 
between  the  results  of  such  tests  and  the  actual  quality  of  the 
cement.  It  would  be  easy  to  select  examples  illustrating  the 
harmony  between  short  and  long  time  tests;  but  it  will  be  of 
greater  value  to  show,  rather,  some  of  the  many  exceptions  to 
such  a  rule,  and  thereby  emphasize  the  fact  that  it  is  only  by 


138 


CEMENT  AND  CONCRETE 


a  close  analysis  of  all  of  the  information  obtainable  concerning 
a  sample,  and  a  general  knowledge  of  the  behavior  of  the  dif- 
ferent grades  of  cement,  that  one  may  hope  to  arrive  at  a  tol- 
erably accurate  opinion. 

226.  Comparative  Tests  of  Portland  Cements.  —  In  Table 
40  are  given  the  results  of  tests  on  four  brands  of  Portland 
cement  at  seven  days,  twenty-eight  days  and  two  years.  From 
the  tests  at  two  years  it  appears  that  T  and  U  are  the  best 
cements,  V  is  nearly  as  good,  but  W  gives  a  much  lower  result. 
Turning  now  to  the  seven  and  twenty-eight  day  tests  of  bri- 
quets maintained  at  the  ordinary  temperature,  it  is  seen  that 
W  gave  in  every  case'  higher  results  than  T,  and  nearly  as  high 
as  U  or  V.  Among  the  short  time  tests  it  is  only  the  results 
of  briquets  maintained  at  80°  C.  that  indicate  the  inferiority 
of  Brand  W. 

TABLE   40 

Interpretation  of   Short   Time   Tests   of  Portland   Cement,  Several 

Brands 


TENSILE  STRENGTH,  POUNDS 

PARTS 
SAND  TO  1 
CEMENT 

BY 

TEMPERA- 
TURE WATER 

OF 

AGE  OF 
BRIQUETS. 

PER  SQUARE  INCH. 

Brand. 

WEIGHT. 

IMMERSION. 

T 

U 

V 

W 

2 

Hot,  80°  C. 

7  days 

339 

278 

284 

222 

3 

a              a 

' 

221 

191 

180 

134 

3 

"     60°  C. 

( 

144 

142 

169 

144 

0 

Ordinary 

' 

420 

510 

487 

565 

1 

c 

327 

425 

400 

396 

2 

( 

172 

275 

256 

236 

3 

t 

73 

150 

160 

150 

1 

28  days 

526 

577 

557 

556 

2 

' 

312 

394 

387 

332 

3 

« 

142 

241 

223 

247 

1 

2  years 

719 

753 

763 

654 

2 

' 

554 

553 

513 

407 

3 

380 

373 

340 

287 

227.  Comparative  Tests  of  Natural  Cements.  —  From  the 
nature  of  natural  cements  a  much  greater  variation  in  strength 
among  different  brands,  and  even  among  different  samples  of 
the  same  brand,  is  to  be  expected.  With  Portland  cements 
made  in  accordance  with  ordinary  methods,  the  variations  in 
strength  among  ten  or  twenty  brands  will  usually  be  compara- 
tively small.  One  of  them  may  possibly  prove  unsound,  and 


1NTERPRETA  T10N 


139 


one  or  two  others  may  give  inferior  strength,  but  the  variations 
in  strength  among  three-fourths  of  the  samples  will  not  gener- 
ally exceed  20  per  cent.  With  the  same  number  of  brands  of 
natural  cements,  variations  of  50  to  200  per  cent,  may  be 
expected. 

TABLE    41 

Interpretation   of    Short  Time  Tests   of  Natural   Cement,   Several 

Brands 


TENSILE  STRENGTH,  POUNDS 

PKK  SQUARE  INCH. 

PARTS 
SANI>  TO  1 
CEMENT. 

TEMPERA- 
TITRE  WATKK 

OF 

A<;rc  <»K 
BRIQUETS. 

Brand. 

I  M  M  K  K  S  I  (  )  N  . 

Jn 

Hn 

Bn 

Mn 

Nn 

Kn 

2 

Hot,  50°  C. 

7  days 

152 

192 

84 

133 

160 

277 

2 

Hot,  60°  C. 

170 

270 

79 

154 

164 

254 

2 

Hot,  80°  C. 

58 

136 

128 

179 

16(5 

221 

0 

Ordinary 

174 

203 

130 

189 

210 

189 

1 

125 

108 

103 

164 

169 

164 

0 

28  days 

208 

344 

25>3 

203 

316 

289 

1 

237 

342 

247 

247 

252 

385 

2 

132 

223 

148 

158 

184 

217 

3 

64 

113 

85 

93 

104 

101 

1 

2  years 

177 

271 

358 

631 

065 

532 

2 

106 

157 

195 

515 

550 

561 

3 

99 

130 

117 

340 

328 

372 

In  Table  41  six  brands  of  natural  cement  are  compared  by 
tests  at  seven  days,  twenty-eight  days  and  two  years.  These 
six  brands  have  been  arranged  in  the  table  according  to  their 
value  as  shown  by  the  two  year  tests,  and  it  is  seen  that  the 
first  three,  Jn,  Hn  and  Bn,  are  especially  poor,  while  the  last 
three,  Mn,  Nn  and  Kn,  are  exceptionally  good.  In  the  short 
time  tests  of  briquets  maintained  at  ordinary  temperature,  Jn 
and  Bn  gave  low  results  and  Nn  and  Kn  gave  fairly  high  results, 
in  harmony  with  the  long  time  tests;  but  Hn,  which  proved  to 
be  one  of  the  poorest  samples,  gave  in  every  case  the  highest, 
or  next  to  the  highest,  result  in  seven  and  twenty-eight  day 
cold  tests.  In  this  table  we  find  again  that  the  results  of  the 
briquets  maintained  at  80°  C.  for  seven  days  gave,  in  a  general 
way,  the  best  indication  of  the  relative  values  of  the  six  brands. 

228.  Several  Samples  of  One  Brand.  —  To  show  that  short 
time  tests  do  not  always  indicate  the  relative  values  of  several 
samples  of  cement,  even  when  all  of  the  samples  are  of  the 


140 


CEMENT  AND  CONCRETE 


same  brand,  Tables  42  and  43  are  given.  All  of  the  results  in 
these  tables  are  from  samples  of  the  one  brand  of  natural  ce- 
ment. 

TABLE  42 

Comparison  of  Short  and  Long  Time  Tests  of  Samples  of  One 
Brand  of  Natural  Cement 


SERIES. 

SAND. 

AGE. 

TENSILE  STRENGTH,  LBS. 
PER  SQUARE  INCH. 

Kind. 

Parts  to 
1  Cement. 

A 

0 
0 

28  days 
6-7  months 

Number 
of  Samples 
Tested. 

3 

7 

2 

3 

5 

•      • 

84 
121 

123 

186 

177 
241 

220 
301 

297 
381 

B 

Std. 

1 
1 

7  days 
6  months 

Number 
Samples. 

17 

20 

74 

4(58 

50 

17 

16 

62 
462 

86 
442 

146 

367 

C 

P.P. 

u 

u 

1 

1  and  2 

2 

7  days 
6  months  * 
7  days  2 

Number 
Samples. 

50 

19 

19 

•      • 

49 
473 

273 

54 
426 
249 

73 
381 

265 

128 
321 
283 

•   • 

D 

P.P.  ' 

0 
2 

2 

7  days 
1  year 

7  days  2 

Number 
Samples. 

13 

48 

38 

18 

•      • 

66 
473 

257 

80 
422 
234 

95 
377 

277 

147 
325 
215 

.  . 

E 

.     .     . 

0 

2 

7  days 
6  months 

Number 
Samples. 

12 

21 

18 

9 

•      • 

74 
535 

83 

477 

120 
424 

167 
373 

•  • 

F 

(  Cr.Qtz.  ) 
\  20  to  40  ( 

0 
2 

28  days 
(  6  months   ) 
(  and  1  year  ] 

Number 
Samples. 

287 

170 

41 

•      • 

135 
565 

191 
454 

235 

367 

.  * 

1  Mean  one-to-one  and  one-to-two  mortars. 

2  Briquets  immersed  six  days  in  water  maintained  at  60°  C. 


INTERPRET  A  TION  141 

In  Table  42  the  results  are  selected  from  a  large  number  of 
tests  of  this  brand,  and  are  arranged  in  groups  according  to  the 
strength  shown  at  a  certain  age.  For  instance,  in  Series  A 
the  results  of  twenty  samples  are  given,  arranged  according  to 
the  strength  at  twenty-eight  days.  Three  of  the  samples  gave 
less  than  100  pounds  per  square  inch,  neat,  at  twenty-eight 
days;  the  same  three  samples  gave  a  mean  strength  of  121 
pounds  per  square  inch,  neat,  six  to  seven  months.  Seven 
samples,  the  strength  of  which  fell  between  100  and  150  pounds 
at  twenty-eight  days,  gave  a  mean  strength  of  186  pounds  at 
six  to  seven  months.  The  results  of  this  series  show  the 
harmony  between  short  and  long  time  tests  when  it  is  a  question 
of  comparing  neat  cement  mortars. 

In  Series  D  of  this  table  the  samples  are  arranged  in  order 
according  to  the  strength  developed  by  one-to-two  mortars 
one  year  old.  Thirteen  samples  had  a  strength  at  this  age  of 
between  450  and  500  pounds,  average  473  pounds.  The  same 
samples  gave  but  66  pounds,  neat,  seven  days.  Forty-eight 
samples,  giving  between  400  and  450  pounds,  average  422 
pounds,  gave  but  80  pounds,  neat,  seven  days,  while  eighteen 
samples  that  developed  only  300  to  350  pounds  mean,  325 
pounds  at  one  year,  showed  a  mean  strength  of  147  pounds,  neat, 
seven  days. 

A  little  study  of  this  table  will  show  that  the  samples  which 
were  comparatively  weak  in  seven  and  twenty-eight  day  tests, 
either  neat  or  with  sand,  gave  the  best  results  in  the  long  time 
tests  of  sand  mortars.  Series  A  shows  that  the  neat  tests  at 
seven  days  and  at  six  months  are  consistent,  but  in  all  cases 
where  sand  mortars  are  tested  at  six  months  to  one  year,  the 
highest  results  are  given  by  the  samples  showing  the  lowest 
strength  in  the  short  time  tests  in  cool  water.  It  is  very  sel- 
dom that  this  conclusion  has  not  been  indicated  by  the  author's 
tests  of  this  brand.  It  is  not  invariably  true,  however,  for 
some  samples  which  were  selected  as  being  defective  in  burn, 
gave  low  results  both  in  short  and  long  time  tests.  The  con- 
clusion stated  above  must  therefore  be  understood  to  have 
limits  even  for  this  brand,  and  may  not  apply  at  all  to  many 
brands. 

As  to  the  results  of  short  time  tests  of  briquets  stored  in  hot 
water,  Series  C  and  D  indicate  that  such  results  are  more  nearly 


142 


CEMENT  AND  CONCRETE 


consistent  with  the  long  time  tests,  yet  it  is  evident  that  even 
with  hot  tests  one  could  not  readily  and  accurately  differen- 
tiate the  best  from  the  mediocre  samples. 

TABLE    43 

Natural  Cement :  Rate  of  Increase  in  Strength,  Hardening  in  "Water 

and  Dry  Air 


TENSILE  STRENGTH  PER  SQ.  IN.,  OF  SAMPLES. 

SAND,  PARTS 
TO  ONE 
CEMENT. 

AGE  OF 
BRIQUETS 
WHEN  BROKEN. 

Hardened  in  Water. 

Hardened  in  Air  of 
Itoom  . 

84 

U' 

O' 

84 

U' 

0' 

1 

7  days. 

74 

53 

103 

107 

68 

187 

1 

28  days. 

228 

189 

228 

188 

95 

256 

1 

3  111  os. 

415 

345 

331 

158 

100 

248 

1 

0  mos. 

500 

381 

307 

425 

161 

359 

1 

2  years. 

446 

383 

209 

151 

147 

403 

3 

28  days. 

99 

97 

64 

112 

61 

180 

3 

3  mos. 

244 

241 

129 

153 

81 

194 

3 

0  mos. 

255 

232 

162 

92 

69 

173 

3 

1  year. 

274 

264 

186 

229 

70 

144 

3 

2  years. 

258 

268 

167 

274 

152 

228 

Sample 

Fineness  :    Per  cent,  passing  Sieve  No.  120,  Holes 

.0046  inch  square 

Time  Setting — to  bear  ^"  £  Ib.  Wire,  min.  .     .     . 
Specific  Gravity 


84   U'    O' 

80.5   87.8  89.7 

54    23  97 
3.012  2.950  3.145 


U',  underburned,  O',  overburned.     All  samples  same  brand,  Gn. 

229.  The  results  in  Table  43  will  serve  to  illustrate  the  same 
point  by  showing  the  very  different  rates  of  increase  in  strength 
of  three  samples  when  the  briquets  are  stored  in  water  and  in 
dry  air.  One  of  these  samples,  84,  was  taken  at  random  from  a 
shipment,  while  U'  and  O'  were  supposed  to  be  defective  in 
burn.  Of  the  water-hardened  specimens,  No.  84  gained  in 
strength  up  to  six  months  or  one  year  and  then  suffered  only 
a  slight  falling  off.  The  underburned  sample  showed  a  con- 
tinuous gain,  but  the  overburned  cement  showed  a  marked 
decrease  in  strength  after  six  months  or  one  year.  The  air- 
hardened  specimens  were  very  irregular  in  strength,  but  the 
underburned  sample  gave  very  low  results  throughout. 

Table  44  gives  similar  results  obtained  with  several  samples, 
the  briquets  being  hardened  in  water  as  usual,  16  R  is  a  fair 


INTERPRETATION 


143 


sample  of  the  best  cement  of  this  brand,  and  its  rate  of  increase 
in  strength  with  one  to  three  parts  sand  is  shown.  Samples 
M  and  L  were  tested  together,  as  were  CC  and  DD.  M  and 
CC  are  of  the  class  giving  comparatively  high  results  at  seven 
days,  while  L  and  DD  give  high  results  at  seven  days,  but 
develop  only  a  moderate  ultimate  strength. 

TABLE   44 

Natural    Cement:    Difference    in   Rates  of   Increase  in   Strength   of 
Several  Samples  of  the  Same  Brand 


H 

CKMKXT. 

SAX  i). 

TEXSILK  STKKXGTH,  POUNDS  I»KK  Scj.  Jx. 
AT  AGK  OF 

s 

!*>  . 

H 

-3 

p2 

4-    ~ 

03 

£ 

s 

§ 

V) 

i* 

2 

H 
*v 

el 

w 

3 

CC 

Kind. 

|l! 

ce 
•o 

c« 
^ 

a 

S 

CO 

I 

! 

CO 

1 

(  11 

16  R 

Crushed  Qtz.  20-30 

1 

04 

142 

334 

300 

430 

500 

445 

2 

u 

u 

2 

50 

101 

280 

341 

335 

386 

354 

3 

(t 

u 

3 

73 

204 

243 

252 

268 

262 

248 

4 

1ST 

0 

118 

100 

^56 

?48 

300 

5 

T, 

0 

40 

88 

148 

146 

167 

6 

M 

Point  aux  Pins 

2 

63 

155 

216 

941 

7 

L 

2 

30 

150 

206 

415 

360 

8 

CC 

t 

1 

123 

232 

276 

260 

317 

9 

DD 

i 

1 

77 

218 

327 

337 

474 

10 

CC 

i 

2 

185 

268 

242 

270 

270 

It 

DD 

i 

2 

180 

326 

303 

373 

350 

230.  Conclusions.  —  From  the  above  tables  one  should  not 
draw  the  conclusion  that  all  strength  tests  are  valueless  be- 
cause likely  to  be  misleading.  Some  lessons,  however,  seem  to 
be  plain;  conclusions  drawn  from  the  results  of  short  time  tests 
of  strength  alone  are  likely  to  be  far  from  infallible.  This  is 
especially  true  of  natural  cements.  The  correctness  of  one's 
conclusions  concerning  the  value  of  a  sample  is  likely  to  de- 
pend very  much  upon  his  knowledge  of  the  behavior  of  that 
particular  brand,  and  the  beginner  in  cement  testing  should 
not  have  too  great  confidence  in  his  early  conclusions.  Samples 
under  inspection  should  be  tested  in  comparison  with  other 
samples  of  known  quality,  and  the  results  of  the  strength  tests 
studied  in  connection  with  all  the  information  obtainable  from 
the  other  tests  of  quality  already  outlined. 


CHAPTER  X 

« 

THE  RECEPTION  OF  CEMENT  AND  RECORDS  OF  TESTS 

ART.  27.     STORING  AND  SAMPLING 

231.  STORAGE.  —  The  storage  houses  provided  for  the    ce- 
ment should  be  such  as  will  effectually  preserve  it  from  damp- 
ness, the  floor  being  dry  and  strongly  built.     A  circulation  of 
air  under  the  floor  will  insure  dryness. 

In  building  houses  for  storage,  due  regard  should  be  given 
to  the  ease  of  getting  the  cement  in  and  out,  and  facilities  pro- 
vided for  the  use  of  block  and  tackle  in  tiering. 

When  the  cement  is  received,  whether  in  sacks  or  barrels,  it 
should,  if  possible,  be  so  tiered  in  the  warehouse  that  any  pack- 
age is  accessible  for  sampling.  In  the  case  of  barrels  this  may 
readily  be  attained  by  tiering  in  double  rows,  the  barrels  lying 
on  the  side.  It  has  been  found  that  ordinary  cement  barrels 
will  withstand  the  pressure  if  tiered  five  high  with  a  " binder" 
row  on  top;  and  when  so  piled,  a  warehouse  32  feet  wide  and 
100  feet  long  will  readily  hold  2,200  barrels,  an  allowance  of 
about  one  hundred  fifty  square  feet  of  floor  space  for  one  hun- 
dred barrels. 

232.  Where  storage  space  is  limited,   the  barrels   may  be 
numbered  and  sampled  before  they  are  placed  in  the  warehouse, 
and  they  may  then  be  piled  solid,  but  this  should  be  avoided 
if  practicable.     Sacks   cannot  be  quite  so   neatly  stored,   and 
since  a  smaller  quantity  is  contained  in  a  sack,  they  may  be 
tiered  so  that  every  third  or  fourth  sack  is  accessible.     It  is 
desirable  where  work  is  executed  with  the  greatest  care  that 
every  package  be  numbered  for  future  identification,  but  this 
may  sometimes  prove  impracticable,   especially  when  the   ce- 
ment is  in  sacks,  and  in  such  cases  the  sampled  packages  only 
may  receive  numbers. 

233.  Percentage  of  Barrels  to  Sample.  —  The  amount  of  ce- 
ment which  shall  be  accepted  on  the  test  of  a  single  sample 
must  be  determined  by  each  user  of  cement  according  to  his 

144 


STORING  AND  SAMPLING  145 

knowledge  as  to  the  uniformity  and  reliability  of  the  brand  in 
use,  and  according  to  the  character  of  the  work  in  which  the 
cement  is  to  be  used.  In  a  few  isolated  cases  every  barrel  is 
tested,  while  sometimes  several  tons  of  cement  are  accepted  on 
a  single  test.  As  the  improvements  in  methods  have  decreased 
the  work  involved  in  making  the  simpler  tests,  the  tendency 
has  been  to  test  a  larger  percentage  of  the  packages.1 

The  report  of  the  committee  of  the  Amer.  Soc.  C.  E.  in 
1SS5,  contains  the  following  concerning  sampling:  " There  is  no 
uniformity  of  practice  among  engineers  as  to  the  sampling 
of  the  cement  to  be  tested,  some  testing  every  tenth  barrel, 
others  every  fifth,  and  others  still  every  barrel  delivered.  Usu- 
ally, where  cement  has  a  good  reputation,  and  is  used  in  large 
masses,  such  as  concrete  in  heavy  foundations,  or  in  the  back- 
ing or  hearting  of  thick  walls,  the  testing  of  every  fifth  barrel 
seems  to  be  sufficient;  but  in  very  important  work,  where  the 
strength  of  each  barrel  may  in  great  measure  determine  the 
strength  of  that  portion  of  the  work  where  it  is  used,  or  in 
the  thin  walls  of  sewers,  etc.,  every  barrel  should  be  tested, 
one  briquet  being  made  from  it." 

234.  Taking  the  Sample.  —  The  sample  should  be  taken  in 
such  a  manner  as  to  fairly  represent  the  package,  and  for  this 
purpose  a  " sugar  trier"  may  be  used,  by  which  is  obtained  a 
core  of  cement  about  one  inch  in  diameter  and  eighteen  inches 
long.  As  any  tool  used  for  boring  cement  barrels  soon  becomes 
dull,  and  as  a  sugar  trier  is  somewhat  difficult  to  sharpen,  the 
author  prefers  to  use  an  ordinary  bit  and  brace  to  penetrate 
the  barrel  head,  and  then  extract  the  sample  with  a  "  trier," 
or  a  long,  slender  scoop  of  similar  form  provided  with  a  handle. 

For  storing  the  sample  until  it  is  tested,  it  has  been  found 
convenient  to  use  covered  tin  cans  holding  about  one  pint, 
the  cover  of  the  can  being  labeled  with  the  number  of  the  pack- 
age from  which  the  sample  is  taken. 


1  In  a  paper  read  before  the  Institution  of  Civil  Engineers  in  1865-66,  Mr. 
John  Grant  states  that  "  after  using,  during  the  last  six  years,  more  than 
70,000  tons  of  Portland  cement,  which  has  been  submitted  to  about  15,000 
tests,  it  can  be  confidently  asserted  that  none  of  an  inferior  or  dangerous 
character  has  been  employed  in  any  part  of  the  work  in  question. "  (The 
Metropolitan  Main  Drainage,  London.)  This  is  an  average  of  one  test  to 
twenty-five  barrels. 


146  CEMENT  AND  CONCRETE 

ART.  28.     RECORDS  OF  TESTS 

235.  Value  of  Records.  —  In  conducting  work  in  which  the 
use  of  cement  enters  as  a  prominent  factor,  it  is  not  only  neces- 
sary to  know  that  the  cement  used  is  of  a  good  quality,  but  also 
to  be  able  to  show  at  any  future  time  what  tests  were  made  to 
establish  its  value.     This  fact,   as  well  as  the   convenience  of 
the  work,  demands  that  a  record  shall  be  kept  of  all  the  tests 
made.     These  records  may  be  more  or  less  elaborate,  according 
to  the  kind  and  amount  of  the  work  in  hand,  but  in  any  case, 
enough  detail  should  be  given  to  make  them  intelligible  to  other 
engineers. 

236.  Marking  Specimens.  —  There  is   sometimes  a  tempta- 
tion, in  making  tensile  specimens,  to  stamp  upon  them  many 
details  of  the  test,   and  for  this  purpose  an  elaborate   cipher 
system  has  sometimes  been  used.     But  this  method  is  to  be 
strongly   deprecated.     Each  briquet  should   receive  its  proper 
consecutive   number,    as   mentioned   in    §189,    and    the    details 
concerning  it  should  be  placed  in  the  record  book. 

237.  RECORDS  KEPT  AT  ST.  MARYS  FALLS  CANAL.—  In  the 
tests  of  cement  at  St.  Marys  Falls  Canal,  during  the  construc- 
tion of  the  Poe  Lock,  a  system  of  records  was  used  that  gave 
entire  satisfaction.     At  the  time  the  largest  amount  of  cement 
was   being   used   three   molders   were   employed,   each   making 
fifty  briquets  per  day  of  eight  hours.     Over  one  hundred  thou- 
sand briquets  were  made  in  five  and  one-half  years.     Although 
the  system  of  records  used  at  this  point  may  be  more  elaborate 
than  is  often  necessary,  yet  the  system  will  be  described,  and 
certain  modifications  will  be  suggested  for  places  requiring  less 
complete  records. 

238.  Barrel  Records.  —  The  barrels  receive  consecutive  num- 
bers after  they  are  tiered  up  in  the  warehouse.     The  "  receiv- 
ing book"  is  a  simple  transit  book  in  which  are  entered  the 
date  of  the  receipt  of  each  cargo,  the  name  of  the  boat  (or  the 
car  number,  if  shipped  by  rail),  the  brand  of  cement,  the  num- 
ber of  barrels,  the  first  and  last  barrel  number  of  the  cargo  and 
the  warehouse  in  which  the  cement  is  placed.     The  next  book 
to  be  used  is  the  "  barrel  book,"  in  which  the  numbers  of  the 
barrels  are  entered  consecutively  in  a  column  at  the  left,  each 
barrel  being  given  one  line.     This  book  is  also  of  transit  size, 
but  might  well  be  larger.     The  headings  are  given  below. 


RECORDS  OF  TESTS 


147 


SAMPLE    PAGE    OF    "BARREL   RECORD" 


No. 
BBL. 

SAMPLED. 

DEFECTS. 

AC- 
CEPTED. 

RK- 

JECTED. 

ISSUED. 

RE.MABKS. 

88251 

2 
3 

4 

5 
6 

8 
o 

88260 

1 

® 
t-j 

3 

4 
5 

M.    D. 

5     10 

M.  1). 

6  5 

S7  =  4Sf 

M.     D, 

G     13 

M.    D. 

July  25 
July   25 
July   25 

Sept.  27 

July  25 
July   25 
July  25 
July  25 
July   25 

67  =  65# 

5     19 

G  6 
G  5 

G     13 

6     12 

S7  =  102$ 
j  Removed   by 
I  Contractor 

(  87=  32#  I 
I  S7  =  35$  ] 

5     19 

5     26 

•   •   - 

5     19 

5     26 

•   •   • 

July   25 
July   25 
July  25 

Sept.  28 

July  25 
July  25 

5     19 

0  6 
6  5 

6     13 

6     12 

S7  =  105# 
\  Removed  by 
I  Contractor 



j  S7=  40#  I 

}  S7  =  321  ( 

\  :  :  : 

When  the  barrels  are  sampled  and  briquets  made,  the  date 
sampled  is  entered  in  the  second  column  of  the  barrel  record 
book.  The  other  columns  will  be  explained  later. 

239.  Holders'  Records.  —  Separate  sheets  of  paper  ruled  and 
headed  as  shown  on  page  148  are  used  by  the  molders  to  record 
the  details  concerning  the  making  of  briquets. 

Separate  sheets  properly  ruled  and  headed  are  also  given  to 
the  assistants  who  test  time  of  setting  and  fineness.  These 
record  sheets,  when  filled  in  by  the  assistants,  are  copied  the 
following  day  by  the  bookkeeper,  into  the  permanent  "  record 
book."  At  the  end  of  the  month  these  separate  sheets,  con- 
taining original  records  of  work  done,  are  folded  and  filed  for 
future  reference. 

240.  Briquet  Record.  —  The  briquets    are  made  in  sets  of 
ten  for  convenience.     Each  set  is  given  a  page  in  the  "  record 
book/'  as  is  indicated  on  page  149  where  the  form  for  this  book 
is  given.    The  size  of  page  is  9  by  12  inches.    Paper  having  the 
same  ruling  and  column  headings  is  convenient  for  reporting 
tests  to  the  chief  engineer. 

241.  Summary  Book.  —  The  data  for  each  set  of  briquets 
are  copied  from  the  record  book,  in  a  condensed  form,  into  the 
"  summary  book,"  one  line  of  the  latter  containing  a  page  of 
the  former.     In  the  summary  book  each  brand  is  given  a  few 


148 


CEMENT  AND  CONCRETE 


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151 


pages  by  itself,  so  that  this  book  corresponds  to  a  ledger  in  form. 
By  this  means  a  large  number  of  tests  on  the  same  brand  may 
be  looked  over  at  once.  The  summary  book  might  be  omitted 
where  a  smaller  number  of  tests  are  to  be  made,  or  it  might 
be  slightly  modified  and  take  the  place  of  the  record  book.  A 
sample  page  is  given  below. 

242.  Records  of  Fineness,  Time  of  Setting  and  Soundness.  - 
Although  provision  is  made  in  the  record  book  for  recording 
time  of  setting  and  fineness,  it  has  been  found  that  where  a 
large  amount  of  cement  is  being  tested  it  is  more  convenient 
to  have  separate  books  for  each  test.  Especially  is  this  true 
as  it  has  been  judged  necessary  to  test  but  a  very  small  per- 
centage of  the  barrels  for  fineness,  while  a  larger  percentage  of 
the  barrels  are  tested  for  time  of  setting  and  soundness.  The 
" fineness  book"  is  as  simple  as  possible  and  need  not  be  illus- 
trated. A  sample  page  of  the  "pat  book"  is  given  below. 

Sample  Page  of  "Pat   Book"    or    Record    of   Time    of    Setting  and 

Soundness 

Lagerdorfer  Portland  Cement  Pats,  Two  from  Ever//  Third  liarrel 


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RECORDS  OF  TESTS  153 

243.  The  Diary.  —  When  the  bookkeeper  has  copied  the 
data  contained  on  the  record  blanks  into  the  record  book  and 
summary  book,  he  turns  to  the  proper  page  in  the  diary  and 
records  the  briquets  to  be  broken.  Thus,  if  briquets  made 
May  17th  are  to  be  broken  at  three  months,  he  enters  the  num- 
bers of  these  briquets  and  the  tank  in  which  they  have  been 
placed  under  the  date  Aug.  17th.  This  leaves  no  chance  of 
allowing  briquets  to  go  beyond  the  proper  time  of  breaking. 

244.  Acceptance  or  Rejection.  —  If  all  of  the  tests  on  a  given 
sample  are  satisfactory,  the  date  of  acceptance  is  placed  in  the 
proper  column  of  the  barrel  book.     It  only  remains  then  to 
mark  the  barrels  "O.  K.,"  and  issue  them  when  needed,  placing 
the  date  of  issue  in  the  column  indicated.     If,  however,  some 
of  the  tests  have  given  unsatisfactory  results,   the  failure  is 
noted  in  the  " defects"   column  of  the  barrel  book,  and  the 
barrel  is  resampled  to  determine  whether  the  failure  was  due  to 
faulty  manipulation.     If  finally  rejected,  the  barrel  is  promi- 
nently marked  to  prevent  its  being  issued  for  use. 

It  is  seen  from  the  above  that  the  history  of  each  barrel  is 
given  in  the  barrel  book,  and  the  record  of  any  brand  is  given 
in  a  condensed  form  in  the  summary  book. 

245.  Special  Tests.  —  When  special  tests  are  made  to  inves- 
tigate  the   effects   of  variations   in   manipulation,   or  for  any 
other  special  purpose,  such  as  to  test  the  value  of  certain  kinds 
of  sand,  it  becomes  convenient  to  have  still  another  form  which 
may  be  called  a  " series  book."     In  this  the  results  are  so  ar- 
ranged that  they  may  be  studied  for  conclusions,  and  tables 
for  reports  may  be  copied  directly  from  it.     A  sample  form  is 
given  on  preceding  page.      Should    extra    rulings  be  needed, 
they  may  be  placed  at  the  right  in  the  "remarks"  column. 


PART  III 

PREPARATION    AND    PROPERTIES   OF 
MORTAR   AND    CONCRETE 


CHAPTER  XI 

SAND  FOR  MORTAR 

246.  Mortar.  —  When  cement  is  mixed  with  sand  and  water, 
the  resulting  paste  is  called  mortar.     The  term. " neat  cement 
mortar"  is  sometimes  used  to  designate  a  cement  paste  with- 
out sand,  but  when  the  term  mortar  is  not  qualified,  it  refers 
to  the  mixture  containing  sand.     The  primary  function  of  mor- 
tar is  to  bind  together  pieces  of  stone  of  greater  or  less  size, 
though  it  is  sometimes  used  alone  to  prevent  the  percolation  of 
water,  to  make  a  smooth  exterior  finish,  or  in  places  too  confined 
to  permit  of  placing  concrete. 

There  are  comparatively  few  cases  in  which  it  is  judicious 
to  use  cement  without  the  addition  of  sand,  for  such  an  ad- 
mixture not  only  cheapens  the  mortar,  but  actually  improves 
it  for  nearly  all  purposes.  The  quality  of  sand  used  is  only 
second  in  importance  to  the  quality  of  the  cement.  Indeed,  if 
one  does  not  know  how  to  select  either  a  good  cement  or  a  good 
sand,  he  is  in  greater  danger  of  going  amiss  in  the  selection  of 
the  latter  than  the  former;  for  the  cement  has  been  placed  upon 
the  market  by  a  manufacturer  who  has  a  reputation  to  estab- 
lish or  maintain. 

ART.  29.     CHARACTER  OF  THE  SAND. 

247.  Various  kinds  of  rock  are  capable  of  producing  sand  of 
good  quality.     The  natural  sands  are  usually  siliceous  in  char- 
acter, but  calcareous  sands  are  also  met  with  and  may  give 
excellent  results  in  mortar.     Good  artificial  sand  may  be  made 
from  almost  any  kind  of  rock  that  is  not  liable  to  chemical 

154 


CHARACTER  OF  SAND 


155 


decay,  even  though  it  be  only  moderately  hard.  One  of  the 
most  essential  features  of  a  good  sand  is  that  the  grains  should 
be  perfectly  sound.  Evidences  that  chemical  decay  is  going 
on  in  the  grains  would  indicate  that  the  sand  is  of  very  inferior 
quality. 

248.  SHAPE  AND  HARDNESS  OF  THE  GRAINS.—  it  is  gener- 
ally believed  that  the  grains  of  sand  should  be  angular  in  order 
to  give  the  best  results;  this  is  probably  true,  although  in  test- 
ing three  varieties  of  calcareous  sand,  M.  Paul  Alexandre  *  ob- 
tained results  which  seemed  to  indicate  that  if  rounded  grains 
are  disadvantageous,  the  other  properties  of  the  sand  may 
readily  counterbalance  this  disadvantage. 

M.  Alexandre  used  three  sands  which  were  reduced  to  the 
same  fineness  by  sifting  into  different  sizes  and  then  remixing 
them  in  fixed  proportions  (equal  parts  of  five  sizes).  The  three 
sands  were,  1st,  white  marble,  very  hard  with  sharp  corners; 
2d,  moderately  hard  limestone;  and  3d,  chalk,  very  soft  with 
rounded  grains.  The  proportions  used  were  400  kg.  of  cement 
to  one  cubic  meter  of  sand,  the  amount  of  water  varying  from 
twenty-five  to  thirty  per  cent,  of  the  sand,  according  to  the 
amount  required  to  produce  plasticity.  The  tensile  strength  of 
the  mortars,  in  pounds  per  square  inch,  is  given  in  Table  45. 

TABLE   45 
Results   Obtained  with  Three   Varieties   of  Calcareous  Sand 


CHARACTER  OF  SAND. 

TENSILE  STRENGTH,  POUNDS 
PEU  SQUARE  INCH  AT 

7  da. 

28  da. 

6  mo. 

H  y™. 

1.  Marble    

45 
72 

86 

107 
148 
120 

171 
222 

205 

220 

256 
252 

3   Chalk 

As  these  sands  varied  in  the  structure  and  hardness  as  well 
as  in  the  shape  of  the  grains,  it  cannot  be  concluded  that  rounded 
grains  are  as  good  as  sharp  and  angular  ones  for  mortar-making. 
There  is  little  question  that  if  two  samples  of  pure  quartz  sand, 


1  "Recherches  Experimentales  sur  Les  Mortiers  Hydrauligues 


156 


CEMENT  AND  CONCRETE 


differing  in  sharpness  but  alike  in  all  other  respects,  including 
the  percentage  of  voids,  were  tested  side  by  side,  the  rounded 
grains  would  be  found  inferior.  (See  also  §  253.) 

M.  Alexandre  also  made  tests  on  sands  differing  both  in 
chemical  and  physical  characteristics,  but  having  the  same  fine- 
ness, namely,  twenty  per  cent,  each  of  five  sizes  of  grain.  Some 
of  the  results  are  given  in  Table  46. 

TABLE   46 

Results   Obtained  with  Various   Sands 


SAND. 

WATER 
PER 
CENT.  OF 
VOLUME 
OF  SAND. 

TENSILE  STRENGTH,  IN  LBS.  PER 
SQ.  IN.,  OF  MORTARS  CONTAIN- 
ING 400  KG.  OF  CEMENT  TO  1  Cu. 
METER  SAND,  AT  AGES  OF 

7  da. 

lyr. 

3  yrs. 

Sea  Sand  .     . 

21 
28 
21 
20 
20 
28 

69 
78 
65 
63 
79 
35 

165 
198 
168 
174 
178 
99 

245 

267 
201 
215 
244 
132 

Calcareous  (Renville  stone)  . 
Granitic     

Siliceous  (cliff  quartz)  
Siliceous  (Cherbourg  Quartzites)   . 
Coke 

249.  Siliceous    vs.    Calcareous    Sands.  —  The    above    tests 
would  seem  to  show  that  sand  to  be  used  in  mortar  need  not  be 
siliceous.     In  experimenting  on  different  varieties  of  sand,  both 
natural   and    artificial,    the   author   has   obtained   results   that 
point  to  a  similar  conclusion.     Some  of  these  tests  are  given  in 
Tables  47  to  50. 

Table  47  gives  the  results  obtained  with  four  varieties  of 
siliceous  sand.  The  first  was  an  artificial  sand  made  by  crush- 
ing sandstone,  the  second  and  third  were  natural  sands  con- 
taining a  large  percentage  of  quartz  grains,  and  the  fourth 
appeared  to  be  almost  pure  quartz.  Only  the  fine  particles  of 
the  sands  were  used  in  the  tests  given  in  this  table.  The  dif- 
ferences in  strength  at  the  end  of  two  years  are  not  great,  but 
the  two  natural  sands  appear  to  give  somewhat  lower  results. 

In  Table  48  the  two  natural  sands  were  again  compared, 
but  this  time  in  connection  with  a  calcareous  sand  formed  by 
crushing  limestone.  The  latter  gave  the  best  results.  Only 
the  finer  grains  were  used  in  these  tests. 

250.  Tables  49  and  50  are  more  valuable  in  this  connection, 


CHARACTER  OF  SAND 


157 


TABLE   47 

Values   of  Different   Varieties  of  Fine   Siliceous   Sand  for  Use  in 
Portland  Cement  Mortar 

Two  PARTS  SAND  TO  ONE  CEMENT  BY  WEIGHT 


REFERENCE. 

SAND. 

FINENESS. 

WATER, 

Per 
Cent. 

TENSILE 
STRENGTH,  LBS. 
PER  SQ.  IN.  AT 

6  Mo. 

2Yr. 

a 

b 

c 

d 

€ 

1 
2 

(  Screenings  from  ( 
crushing  Pots-  j 
(      dam  sandstone  ( 

Pass  40  sieve  . 
Pass  40  sieve, 
retained  on  100 

18.5 
17.5 

388 
478 

470 
539 

3 

Bank  sand,  siliceous 

Pass  40  sieve  . 

13.3 

433 

445 

4 

River  sand,  siliceous 

Pass  40  sieve  . 

12.1 

382 

437 

5 

Clean  quartz 

Pass  40  sieve  . 

13.3 

398 

606 

NOTE.  —  Holes  in  No.  40  sieve  0.015  inch  square,  holes  in  No.  100  sieve 
about  0.0065  inch  square. 

TABLE  48 
Different  Varieties  of  Fine  Sand  for  Portland  Cement  Mortar 


TENSILE  STRENGTH,  POUNDS 

w 

PER  CENT. 

PER  SQUARE  INCH. 

0 

to 

SAND. 

FINENESS. 

1  Part  Sand  to  1 

2  Parts  Sand  to 

£ 

Cement  by  Wt. 

Cement  by  Wt. 

1  tol 

1  to2 

6  mo. 

13 
mo. 

3yr. 

6  mo. 

18 
mo. 

3yr. 

a 

6 

c 

d 

e 

/ 

9 

h 

i 

J 

1 

River  sand,  sili- 

ceous     .     .    . 

Pass  40  sieve 

14.0 

12.4 

715 

725 

776 

491 

575 

581 

2 

Bank  sand,  sili- 

ceous     .    .     . 

Pass  40  sieve 

14.5 

12.6 

664 

699 

759 

442 

502 

5?4 

3 

Calcareous  sand 

from  crushing 
limestone   .     . 

Pass  40  sieve 

18.2 

17.7 

721 

770 

788 

531 

632 

(580 

4 

Calcareous  sand 
from  crushing 
limestone  .     . 

Pass  40,  re- 
tained on  100 

17.5 

17.0 

753 

783 

844 

597 

659 

727 

since  the  coarser  particles  of  the  sand  were  used  with  the  fine. 
The  sand  was  separated  into  four  sizes  by  sifting,  and  then 
remixed  in  equal  proportions.  Table  49  gives  the  results  ob- 


158 


CEMENT  AND  CONCRETE 


tained  with  natural  cement,  and  Table  50  refers  to  Portland. 
The  superiority  of  the  screenings  is  very  clearly  shown,  the 
limestone  giving  especially  good  results.  Indeed,  the  strength 
obtained  with  three  parts  limestone  screenings  to  one  part  of 
either  Portland  or  natural  cement  is  remarkably  high.  The 
mortar  made  from  such  sand  is  peculiarly  plastic  when  fresh, 
and  soon  gains  a  high  strength  which  it  appears  to  maintain. 

TABLE   49 
Values  of   Different  Varieties  of  Sand  for  Natural  Cement  Mortar 


.  ^ 

TENSILE  STRENGTH,  Lus. 

02 

fc  E 

PER  SQ.  IN.,  3  PARTS  SAND 

H 
M 

SAND. 

B 

«£ 

TO  1  CEMENT  BY  WT. 

£ 

£§ 

28  Da. 

6Mos. 

1  Yr. 

2  Yrs. 

a 

» 

c 

d 

e 

/ 

ff 

1 

Clean  crushed  quartz   .     .     . 

MX. 

15.4 

1171 

344 

356 

332 

2 

River  sand,  siliceous     . 

MX. 

13.3 

93 

297 

339 

308 

3 

Limestone  screenings   . 

MX. 

16.7 

143 

467 

526 

601 

4 

Potsdam  sandstone  screenings 

MX. 

18.2 

113 

316 

416 

462 

5 

Clean  crushed  quartz    . 

20-30 

12.5 

118 

330 

342 

324 

1  13.6  per  cent,  water,  trifle  dry. 

NOTE.  —  Fineness  MX.  means  25  psr  cent,  each  of  20-30,  30-40,  40-50 

and  50-80. 
Expression  20-30  means  passing  No.  20  sieve  and  retained  on 

No.  30  sieve. 

TABLE    50 

Values  of  Different  Varieties  of  Sand  for  Portland  Cement  Mortar 


. 

.  . 

TENSILE  STRENGTH,  LBS. 

CO 

fc  w 

PER  SQ.  IN.,  3  PARTS  SAND 

fe 

g 

w  ^ 

TO  1  CEMENT  BY  WT. 

H 

PH 

SAND. 

B 

fc 

«£ 

£ 

^§ 

28  Da. 

6Mos. 

lYr. 

2  Yrs. 

a 

6 

c 

d 

e 

/ 

9 

1 

Clean  crushed  quartz    .     . 

MX. 

12.5 

255 

327 

359 

335 

2 

River  sand,  siliceous     . 

MX. 

11.1 

206 

284 

329 

324 

8 

Limestone  screenings   . 

MX. 

12.  51 

407 

574 

667 

6652 

4 

Sandstone  screenings    .     . 

MX. 

12.  51 

321 

438 

495 

4923 

5 

Clean  crushed  quartz   . 

20-30 

11.1 

259 

344 

369 

335 

1  Trifle  dry,  plastic.     2  13.3  per  cent,  water.     3  14.3  per  cent,  water. 
NOTE.  —  Fineness  MX.  means  25  per  cent,  each  of  20-30,  30-40,   40-50 
and  50-80. 


FINENESS  OF  SAND  159 

251.  Slag  Sand.  —  To   turn   to   good   account  some  of    the 
immense  quantities  of  blast  furnace  slag  produced  yearly,  the 
use  of  granulated  slag  in  place  of  ordinary  sand  has  been  ad- 
vocated.    In   a   paper   read   before   the   Engineers'    Society   of 
Western  Pennsylvania,   in   March,   1904,   Mr.   Joseph  A.   Shinn 
described  some  experiments  he  had  made,  in  which  it  was  shown 
that   "slag  sand,"  with   Portland   cement,    natural   cement,   or 
common  lime,  gave  a  higher  strength  than  the  sample  of  river 
sand  used  in  the  comparison. 

The  "slag  sand"  is  produced  by  projecting  two  flat  jets  of 
water  into  the  stream  of  molten  slag,  the  resulting  sand  being 
heavier,  finer  and  more  nearly  uniform  in  size  of  grain  than  the 
ordinary  slag  granulate. 

252.  Sand  for  Use  in  Sea  Water.  —  It  has  been  said  that 
granitic  sands  when  used  in  sea  water  do  not  give  good  results 
on  account  of  the  felspar  of  the  granite  being  attacked  by  the 
cement  when  the  concrete  is  impregnated  with  sea  water.     M. 
Paul  Alexandre  would  proscribe  the  use  of  argillaceous  sands 
in  sea  water,   but  he  found  that  sands  containing  calcareous 
marl  gave  excellent  results  in  the  sea,  and  others  have  stated 
that  the  mixture  of  crushed  limestone  with  concrete  has  been 
known  to  hinder  the  action  of  sea  water  upon  it.     Since  porous 
and   permeable   mortars   are   most   liable   to   disintegration   by 
sea  water,  it  is  evident  that  it  is  especially  desirable  to  employ 
a  sand  in  which  the  proportion  of  voids  is  small. 

ART.  30.     FINENESS  OF  SAND 

253.  The  size  and  shape  of  the  grains  are  important  ele- 
ments in  the  quality  of  sand.     Considering  grains  of  the  same 
shape  but  differing  in  size,  the  larger  grain  will  have  a  smaller 
surface  area  in  proportion  to  the  volume  than  the  smaller  grain, 
since  the  volume  varies  approximately  as  the  cube  of  one  di- 
mension while  the  surface  varies  as  the  square.     Since,  in  order 
to  obtain  the  best  results  in  mortar,  each  grain  of  sand  must  be 
coated  with  cement,  it  follows  that,  other  things  being  equal, 
the  coarser    grained  sands  will  give  the  best    results,  because 
they  will  be  more  thoroughly  coated;  this  will  be  especially  true 
when  the  amount  of  sand  in  the  mortar  is  relatively  large. 

Following  the  same  reasoning  given  above  as  to  the  relative 
volume  and  superficial  area  of  sand  grains,  it  would  appear 


100 


CEMENT  AND  CONCRETE 


that  spherical  grains  would  be  better  than  cubical  or  angular 
ones  (see  §  248).  This,  however,  is  not  thought  to  be  the  case, 
for  the  better  bond  obtained  with  angular  grains  seems  to  coun- 
terbalance the  advantage  which  the  small  superficial  area  would 
appear  to  give  to  the  spherical  grains.  For  this  reason  a  len- 
ticular shaped  grain,  while  having  a  very  large  area  relative  to 
its  volume,  will  give  excellent  results  in  mortar  if  otherwise 
suited  to  the  purpose. 

It  is  usually  desirable  to  have  all  of  the  voids  in  the  sand 
filled  by  the  cement  paste,  as  this  renders  the  mortar  less  por- 
ous, and  makes  it  more  certain  that  all  the  grains  are  coated 
with  cement.  On  this  account  a  mixture  of  fine  and  coarse 
particles  is  excellent. 

TABLE   51 

Effect   on   Tensile    Strength   of   Varying   Fineness    of  Limestone 
Screenings   Used   with  Portland    Cement 


AGE 
BRIQUETS  WHEN 
BROKEN. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH 
FINENESS  OF  SCREENINGS. 

10-20. 

20-30. 

30-40. 

40-50. 

40-80. 

PASS  50. 

6  months     . 

718 

657 

633 

516 

.    .    .    .. 

403 

2  years  . 

812 

754 

656 

.  .  . 

516 

488 

4  years  .     .     . 

845 

782 

714 

•  ... 

571 

516 

SIGNIFICANCE  OF  FINENESS 


SIEVE  NUMBER. 

APPROXIMATE 

Passing. 

Retained  on. 

GRAIN. 

Inch. 

10-20 

10 

20 

.057 

20-30 

20 

30 

.028 

30-40 

30 

40 

.020 

40-50 

40 

50 

.015 

40-80 

40 

80 

.012 

Pass  50 

50 

.     .     .     . 

.008 

NOTES.  —  Three  parts  screenings  to  one  cement  by  weight. 

All  briquets  made  by  one  molder  and  immersed  in  one  tank. 
Variations  in  consistency  were  slight,  the  largest  percentage  of 
water  being  used  for  the  finest  particles. 


FINENESS  OF  SAND 


161 


254.  TESTS  ON  EFFECT  OF  FINENESS  OF  SAND.  —  Many  of 
the  experiments  made  to  show  the  effect  of  the  fineness  of  sand 
on  the  strength  of  the  mortar  are  defective,  because  the  sand 
used  varies  in  the  shape  of  the  grains  and  in  chemical  charac- 
teristics as  well  as  in  fineness.  The  experiments  given  in  Table 
51  were  made  with  screenings  obtained  in  crushing  limestone, 
and  thus  all  causes  of  variation  aside  from  the  fineness  of  the 
sand  were  absent,,  except  the  differences  in  consistency  of  the 
mortar,  the  uniformity  in  consistency  depending  on  the  judg- 
ment of  the  operator.  The  results  show  quite  clearly  the  su- 
periority of  the  coarser  sand. 

255.   The  Relative  Effect  of  Fine  Sand  on  Portland  and  Nat- 
ural Cement.  —  The  tests  in  Table  52  were  made  to  determine 


TABLE    52 

Coarse    and    Fine     Sand,  —  Relative    Effects    with    Portland     and 

Natural   Cement 


TENSILE 

Q 

TENSILE 

STRENGTH, 

K 

STRENGTH, 

AGE  OK 
BRIQUETS 

WHEN 

m 

POUNDS  PER 
SQ.  IN.  WHEN 
SAND  is 

IP! 

g5K 

i«$. 

POUNDS  PER 
SQ.  IN.  WHEN 
SAND  is 

2S«S 

*%~? 

BROKEN. 

5  2    ^ 

«£*; 

*  H*^ 

20-30 

40-80 

a  92       H 

i. 

20-30 

40-80 

a  02     p 

o 

ft* 

O 

ftn 

28  days    .  .  j 

Bn 

In 

197 

89 

145 

57 

74 

64 

A 

U 

406 
352 

337 
275 

83 
78 

6  mouths  .  .  | 

Bn 
In 

216 
364 

188 
267 

87 
73 

A 
U 

520 
499 

446 
415 

86 
83 

2  years     .  .  j 

Bu 
In 

256 
450 

250 

419 

98 
93 

A 
U 

546 
567 

451 

496 

83 
89 

NOTES. — Sand,   limestone    screenings;    three  parts  to  one   cement    by 

weight. 
20-30  means  sand  passing  sieve  with  20  meshes  per  linear 

inch,   and  retained  on  sieve  with  30  meshes  per  linear 

inch. 
Columns  5  and  9    show   percentage  that    strength    with  finer 

sand  is  of  the  strength  with  coarser  sand. 

the  relative  effects  of  fine  sand  on  Portland  and  natural  cements. 
Limestone  screenings  of  two  sizes  of  grain  were  used  in  con- 
nection with  two  brands  of  each  kind  of  cement.  At  twenty- 
eight  days  the  natural  cement  shows  the  decrease  in  strength 
due  to  the  use  of  fine  sand  more  than  Portland  cement  does. 


162  CEMENT  AND  CONCRETE 

At  six  months  the  fine  sand  seems  to  have  about  the  same 
effect  on  Portland  and  natural,  but  the  two-year  results  in- 
dicate that  the  ultimate  effect  is  less  on  the  natural  cement 
than  on  the  Portland;  the  mean  ratio  of  the  strength  obtained 
with  fine  sand  to  that  given  by  coarse  sand  being  ninety-six 
in  the  case  of  natural,  and  only  eighty-six  in  the  case  of  Port- 
land. The  effect  of  fine  sand  appears  to  decrease  with  age, 
especially  with  natural  cement. 

The  fineness  of  sand  will  be  treated  further  in  the  following 
article  relating  to  voids. 

ART.  31.     VOIDS  IN  SAND 

256.  Conditions  Affecting  Voids.  —  The  voids   present  in   a 
given  mass  of  sand  will  depend  upon  the  shape  of  the  grains, 
the  degree  of  uniformity  in  size  of  grains,  the  amount  of  moisture 
present,  and  the  amount  of  compacting  to  which  the  mass  has 
been  subjected.     If  all  of  the  grains  in  a  given  mass  of  sand  are 
of  uniform  size,  the  percentage  of  voids  will  be  independent  of 
what  that  size   may   be.     In   other  words,   the   percentage   of 
voids  in  a  cubic  foot  of  buckshot  will  be  the  same  as  in  a  cubic 
foot  of  bird  shot;  but  if  we  take  a  cubic  foot  of  a  mixture  of 
buck    and    bird   shot  we    will    find   that    the   voids   are   much 
less. 

257.  Effect  of  Shape  of  Grain.  —  M.  Feret  has  published  in 
France  the  results  of  a  large  number  of  experiments  made  by 
him  as  to  the  voids  in  sand  and  broken  stone.1     Table  53  gives 
the  results  he  obtained  concerning  the  effect  of  the  shape  of 
the  grains  on  the  percentage  of  voids  present.     He  first  divided 
each  sand  into  three  parts  by  means  of  three  sieves,  which  we 
will  call  A,  B  and  C.     Sieve  A  had  four  meshes  per  sq.   cm. 
(about  five  meshes  per  linear  inch),  sieve  B  had  36  meshes  per 
sq.  cm.  (about  fifteen  meshes  per  linear  inch),  and  sieve  C  had 
324   meshes   per   sq.    cm.    (about   forty-five   meshes   per   linear 
inch).     The  grains  that  passed  A  and  were  retained  on  B  were 
designated  G,  the  grains  that  passed  B  and  were  retained  on  C 
were  designated  M,  and  the  grains  that  passed  C  were  desig- 
nated F.     These  different  sizes  were  then  recombined  by  tak- 
ing five  parts  of  G,  three  parts  of  M  and  two  parts  of  F,  and 


Abstracted  in  Engineering  News,  Vol.  XXVII,  p.  310. 


VOIDS  IN  SAND 


163 


the  resulting  sand  was  designated  G5  M3  F2.     Thus,  all  of  the 
sands  tested  had  the  same  "granulometric"  composition. 

TABLE   53 

Voids   in    Sands   Having   Different   Shaped   Grains 
FROM  M.  FERET 


NATURE  OF  SAND. 

VOLUME  OF  VOIDS  REMAINING  IN 
ONE  LITER  OF  SAND. 

Unshaken. 
C.C. 

Shaken  to  Refusal. 
C.C. 

Natural  sand  with  rounded  grains. 
Cherbourg  quart/ite,  angular  grains. 
Crushed  shells,  flat  grains. 
Residue  of  Cherbourg  quartzite  crushed 
between  jaws,  laminated  grains. 

359 

421 
44:) 

475 

256 
274 

318 

346 

It  is  seen  that  the  rounded  grains  have  the  smallest  percent- 
age of  voids,  or  about  thirty-six  per  cent,  unshaken,  while  the 
laminated  grains  gave  the  largest  percentage.  It  may  also  be 
noticed  that  the  angular  grains  were  compacted  more  by  shak- 
ing than  any  of  the  others. 

258.  Effect  of  Granulometric  Composition  of  Sand  on  the 
Percentage  of  Voids.  —  To  determine  the  effect  of  uniformity  of 
size  of  grain  upon  the  percentage  of  voids  and  the  strength  of 
mortars,  the  author  has  experimented  with  an  artificial  sand 
formed  by  crushing  limestone.  That  portion  of  the  product 
that  passed  the  coarse  screen  of  the  crusher  varied  in  fine- 
ness from  particles  three-eighths  of  an  inch  in  one  dimension  to 
a  very  fine  powder,  the  particles  of  which  were  less  than  .0065 
inch  in  one  dimension.  Such  material  admits  of  division  into 
parts  that  differ  widely  in  fineness,  but  which  are  essentially 
of  the  same  composition,  and  it  is  therefore  excellent  for  an 
experiment  of  this  kind. 

The  four  sieves  used  in  first  separating  the  material  into 
parts  had,  respectively,  10,  20,  40  and  80  meshes  per  linear  inch, 
the  sizes  of  the  holes  being,  respectively,  about  as  follows:  0.08 
inch,  0.033  inch,  0.017  inch,  and  0.007  inch  square.  The  sev- 
eral sizes  of  grain  are  designated  as  follows:  — 

"C,"  Coarse,  passing  No.  10,  retained  on  No.  20. 
"M,"  Medium,      "         "  20,  "  "  40. 

"F,"  Fine,  "         "  40,  "  "  80. 

"V,"  Very  fine,    "        "  80. 


164 


CEMENT  AND  CONCRETE 


M.  Feret's  method  of  designating  the  granulometric  compo- 
sition, namely,  to  represent  by  exponents  the  number  of  parts 
of  each  size  of  grain,  has  been  adopted. 

259.  The  voids  were  obtained  by  first  weighing  a  given 
volume  of  the  sand;  dividing  the  weight  by  the  specific  gravity 
of  the  limestone,  as  previously  determined,  gives  the  amount 
of  solid  material  in  the  measure,  and  this  subtracted  from  the 
volume  of  the  measure,  gives  the  voids.  This  method  is  con- 
sidered more  nearly  accurate  than  the  usual  one  of  measuring 
the  amount  of  water  required  to  fill  the  voids  in  a  measure  of 
sand,  especially  so  for  a  sand  of  uniform  character  and  one 
which  absorbs  water  quite  freely. 


TABLE   54 

Voids  in  Limestone  Screenings,  Showing  Effect  of  Variations  in 
GFranulometric  Composition 


FINENESS  OF 
GRAN  ULOMET  RIO 
COMPOSITION. 

WEIGHT  OF 
ONE  LITER  OF 
SAND,  DRV, 
GRAMS. 

VOLUME  SOLID 
SAND  IN 
ONE  LITER 

(SP.  GR.  =  2.667) 
Cu.  CENT. 

PER  CENT. 
VOIDS 
IN  SAND. 

Loose. 

Shaken. 

Loose. 

Shaken. 

Loose. 

Shaken. 

a 

b 

c 

d 

€ 

/ 

9 

C  =  Coarse     10  to  20 

1126 

1358 

422 

509 

57.8 

49.1 

M  =  Medium  20  to  40 

1140 

1362 

428 

511 

57.2 

48.9 

F  =  Fine         40  to  80 

1150 

1392 

431 

522 

56.9 

47.8 

V  =  Very  fine,  pass  80 

1165 

1609 

437 

603 

56.3 

39.7 

C 

1395 

.   .  . 

523 

47.7 

M 

1439 

. 

540 

46.0 

F 

1459 

. 

547 

45.3 

V 

1656 

621 

37.9 

C56,  M25,  F*5,  V* 

1606 

. 

602 

. 

39.8 

C40,  M30,  F2o,  V10 

1732 

649 

. 

35.1 

C25,  M25,  F25,  V25 

1912 

717 

28.3 

C30,  M25,  Fis,  V30 

1850 

. 

694 

, 

30.6 

C50,  M°,  F>,  V5° 

1991 

746 

25.4 

The  results  obtained  are  given  in  Table  54.  Comparing  the 
voids  in  C,  M,  F  and  V,  it  is  seen  that  the  first  three  have  nearly 
the  same  percentage,  but  V  has  less  voids  than  the  others. 
This  is  explained  by  the  fact  that  this  sample  was  made  up  of 
all  sizes  smaller  than  the  holes  in  No.  80  sieve,  down  to  the 
fine  powder.  Comparing  the  mixed  sands,  it  is  seen  that  the 
sample  made  up  of  equal  parts  of  coarse  and  very  fine  had 


VOIDS  IN  SAND 


105 


the  least  voids,  the  percentage  being  only  a  little  more  than 
half  of  that  obtained  with  coarse  particles  alone.  The  next 
lowest  percentage  was  given  by  the  sample  having  equal  parts 
of  four  sizes. 

It  is  apparent  that  the  granulometric  composition  has  a 
very  important  effect  on  the  percentage  of  voids.  When  one 
desires  to  make  a  compact  mortar  with  as  small  a  quantity  of 
cement  as  possible,  similar  tests  might  well  be  made  with  the 
materials  available  for  use. 

260.  Effect  on  Strength  of  Mortars  of  Varying  the  Granulo- 
metric Composition  of  Sand.  —  Table  55  gives  the  results  of 
tensile  tests  of  mortars  made  with  limestone  screenings  of  vari- 
ous granulometric  compositions.  The  differences  in  strength 
are  not  very  great,  but  it  appears  that  with  one-to-three  mor- 
tars the  highest  strength  is  developed  at  six  months,  with  the 
coarse  grains  alone,  but  when  poorer  mortars  are  in  question 
the  result  is  affected  by  the  percentage  of  voids  in  the  sand. 

TABLE    55 

Limestone   Screenings   with   Portland   Cement.    Effect   on   Tensile 
Strength  of  Variations  in  Granulometric  Composition  of  Sand 


TENSILE  STRENGTH  AT 

(i  RANULOMETRIC  COMPOSITION 

6  Mos.    POUNDS  PER 

WEIOHT  OP 

OK  SANI>.    PER 

SQ.  IN.  WITH  PARTS  SAND 

BRIQUETS  IN 

CENT.  OF  EACH  SIZE  GRAIN. 

VOIDS. 

TO  ONE  CEMENT  BY 

GRAMS. 

% 

WEIGHT. 

c 

M 

F 

V 

3 

5 

3 

5 

0 

100 

0 

0 

46 

609 

324 

1465 

1438 

40 

30 

20 

10 

35 

505 

392 

1466 

1480 

25 

25 

25 

25 

31 

470 

356 

1445 

1455 

30 

25 

15 

30 

28 

496 

391 

1448 

1470 

60 

0 

0 

50 

25 

487 

349 

1455 

1460 

CEMENT.  —  Portland,  Brand  R. 
see  text. 


For  significance  of  composition  of  sand, 


261.  Table  56  gives  the  results  of  similar  tests  of  both  Port- 
land and  natural  cement  with  Point  aux  Pins  sand  dredged 
from  St.  Marys  River  and  containing  a  very  large  percentage 
of  quartz  grains.  The  sand  was  divided  into  but  three  parts 
by  sifting,  and  was  then  remixed,  the  proportion  of  each  size 
being  indicated  in  the  table.  The  results  verify  the  conclusions 


166 


CEMENT  AND  CONCRETE 


already  drawn  that  the  coarser  sands  give  the  higher  strength. 
It  appears  that  not  more  than  one-half  of  the  grains  should  be 
very  fine  if  the  best  results  are  desired. 

TABLE   56 

Varying  the  Granulometric  Composition  of  River  Sand.    Effect  on 
Value  of,  for  Use  in  Cement  Mortar 


COMPOSITION  OF  SAND  AS 
TO  FINENESS. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

Parts  Used 
that  Passed 
No.  20  Sieve 
and  Re- 
tained on 
No.  30. 

Parts 
Used, 
30-40 

Parts 
Used  that 
Passed 
No.  40 
Sieve. 

Portland  Cement  Avith 
Two  Parts  Sand  to  One 
Cement  by  Weight,  at 
age  of 

Natural  Cement  with 
Three  Parts  Sand  to  One 
Cement  by  Weight,  at 
age  of 

M 

F 

V 

28  da.  !  6  mo. 

lyr. 

2  yr. 

28  da. 

6  mo. 

lyr. 

2  yr. 

10 

0 

0 

342 

471 

560 

591 

77 

267 

348 

341 

4 

1 

5 

300 

448 

515 

507 

77 

237 

304 

319 

2 

4 

4 

290 

425 

494 

503 

79 

278 

291 

325 

1 

3 

6 

246 

384 

455 

442 

46 

222 

234 

251 

1 

2 

7 

271 

366 

456 

438 

07 

226 

247 

251 

NOTE.  —  River  sand,  mostly  quartz,  obtained  at  Point  aux  Pins.     Each 
result  mean  of  five  briquets,  all  made  by  one  molder. 

262.  Effect  of  Moisture.  —  The  effect  of  a  small  amount  of 
moisture  on  the  bulk  of  a  given  weight  of  sand  is  not  usually 
appreciated,  but  it  may  easily  be  shown  that  it  is  very  marked. 
The  results  in  Table  57  were  obtained  by  adding  small  amounts 
of  water  to  a  given  bulk  of  dry  sand.  Each  time,  after  the 
water  was  added,  the  sand  was  stirred  up  and  the  weight  of  a 
given  volume  of  the  moist  sand  was  obtained.  It  appears  that 
the  finer  sands  are  affected  more  than  coarse  ones. 

In  the  case  of  the  limestone  screenings  40-80,  if  we  add  but 
3.7  per  cent,  water  to  a  given  quantity  of  dry  sand,  the  bulk 
of  the  sand  is  so  increased  that  if  we  take  1,000  c.c.  of  the  moist 
sand  it  will  contain  but  720  c.c.  of  dry  sand.  The  voids  are, 
of  course,  correspondingly  increased  from  54.5  per  cent,  to 
67.2  per  cent. 

The  cause  of  this  increase  in  bulk  is  that  each  grain  of  sand 
is  surrounded  by  a  film  of  water  which  prevents  the  grains 
from  lying  close  together  after  they  have  been  disturbed.  A 
large  amount  of  air  is  also  imprisoned  in  the  mass.  It  may  be 
noticed  that  the 'difference  in  bulk  between  moist  and  dry  sand 
is  greater  when, the  measurements  are  made  "  loose." 


VOIDS  IN  SAND 


167 


TABLE    57 
Volume  of  Sand  and  Voids  as  Affected  by  the  Addition  of  Water 


ERENCE. 

SAND. 

EXPRESSED 
t  CENT.  OF 
SAND  BY 

Kir.HT. 

WEIGHT  OF 
DRY  SAND  IN 
ONE  LITER 
OF  MOIST 
SAND. 

VOLUME  OF 
DRY  SAND 
IN  ONE 
LITER  OF 
MOIST 
SAND. 

PERCENT. 
VOIDS  IN 
SAND  BY 
VOLUME. 

^ 

Kind. 

g 

*£#'* 

«T2 

Cx 

•-  r 

gl 

0 

a 

V 

E 

4  *^ 

c  p 

11 

§~ 

H^ 

0 

5 

£ 

-^ 

"  '3 

C 

JS  3 

* 

33 

a 

b 

c 

rf 

e 

f 

9 

h 

i 

Crushed 

1 

Limestone. 

10-20 

0.0 

1288 

1489 

1000 

1000 

. 

2 

i 

" 

4.8 

1094 

1367 

849 

919 

3 

i 

" 

7.7 

1023 

1295 

794 

869 

4 

i 

" 

11.9 

996 

1276 

773 

857 

. 

5 

« 

40-80 

0.0 

1214 

1481 

1000 

1000 

54.5 

44.6 

6 

c 

" 

0.85 

1124 

1489 

920 

1005 

57.9 

44.2 

7 

I 

u 

1.5 

1059 

1470 

872 

993 

603 

44.9 

8 

' 

(1 

2.2 

950 

1383 

782 

934 

64.4 

48.2 

9 

' 

(i 

3.7 

875 

1298 

720 

877 

67.2 

51.4 

10 

1 

u 

6.3 

824 

1274 

679 

860 

69.1 

52.3 

11 

' 

" 

7.8 

799 

1266 

658 

855 

70.0 

52.6 

12 

' 

" 

12.3 

817 

1280 

672 

864 

69.4 

52.0 

13 

1 

(I 

16.8 

829 

1306 

683 

881 

69.0 

51.1 

14 

« 

u 

20.2 

836 

1274 

689 

860 

68.6 

52.3 

15 

' 

u 

25.3 

891 

1357 

783 

916 

66.6 

49.1 

16 

1 

" 

30.3 

1049 

1270* 

864 

858* 

< 

t 

17 

' 

Pass  80 

0.0 

1185 

1500 

1000 

1000 

18 

' 

" 

2.4 

1038 

1394 

873 

929 

19 

1 

" 

5.1 

835 

1281 

704 

854 

20 

' 

" 

12.2t 

806 

1310 

680 

873 

. 

21 

1 

" 

17.7t 

806 

1260 

680 

840 

Point  aux 

22 

Pins. 

c 

0.0 

1725 

1000 

23 

i 

2.0 

1405 

815 

24 

t 

4.0 

1400 

810 

25 

i 

t  J 

6.0 

1400 

810 

26 

i 

\ 

10.0 

1415 

820 

27 

i 

11.6 

1425 

825 

28 

i 

18.4 

1485 

860 

*  Not  jarred  down  in  measure  as  much  as  usual.     Water  rose  to  surface, 
t  Sand  crumbled  like  damp  earth. 


J  Fineness  of  Point 
aux  Pins  Sand 


r  Sieves  No.                      20  30  40  50  80 
J      Approx.  size 

holes  -  .033  .022  .017  .012  .007 

[Percent,  passing        96.0  82.3  46.6  6.7  1.2 

NOTE.  — 10-20  =  passing  No.  10  sieve  (holes  about  .08  in.  sq.)  and  retained 
on  No.  20  sieve. 


1G8  CEMENT  AND  CONCRETE 

263.  This  subject  is  of  great  importance  in  proportioning 
mortars,  because,  in  construction,  the  amounts  of  cement  and 
sand  are  usually  measured.     Suppose  it  is  desired  to  use  a  mix- 
ture of  one  hundred  pounds  of  cement  to  four  hundred  pounds 
of  sand,  and  for  convenience  we  will  suppose  the  packed  cement 
and  dry  sand  each  weigh  one  hundred  pounds  per  cubic  foot. 
If  now  we  use  damp  sand,  containing  about  3.5  per  cent,  water, 
instead  of  dry  sand,  and  measure  the  materials,  we  would  have 
four  cubic  feet  of  damp  sand  to  one  cubic  foot  of  cement;  but 
damp  sand  would  contain  only  about  4  X  75  =  300  pounds  of 
dry  sand,   and   we   would  really  have   a  one-to-three  mixture 
instead  of  a  one-to-four. 

ART.  32.     IMPURITIES  IN  SAND 

264.  The   usual   specification   for   sand   is   that   it   shall    be 
"  clean,  sharp  and  siliceous."     We  have  shown  that  it  need  not 
be  siliceous,  and  we  have  also  noted  that  one  authority  con- 
siders that  it  need  not  be  sharp,  though  this  latter  does  not 
appear  to  be  proven;  let  us  see  what  interpretation  should  be 
given  to  the  word  " clean"  if  it  must  be  retained  in  all  speci- 
fications for  sand. 

Mr.  E.  C.  Clarke,  in  the  tests  for  the  Boston  Main  Drainage 
Works,  showed  that  "clay  in  moderate  amounts"  (ten  per 
cent,  to  thirty  per  cent,  of  the  sand)  "does  not  weaken  cement 
mortars."  Calcareous  marl  might  be  considered  an  impurity, 
but  we  have  seen  that  M.  Alexandre  found  that  sands  contain- 
ing this  material  gave  excellent  results.  On  the  other  hand, 
there  seems  to  be  no  doubt  that  loam,  peaty  matter  or  humus 
will  very  materially  decrease  the  strength  of  mortars,  or  even 
destroy  them  entirely.  Likewise,  decayed  particles  of  some 
kinds  of  stone,  or  grains  which  readily  break  up  into  thin  scales, 
should  be  strenuously  avoided. 

265.  Detection  of  Impurities.  —  Clean  sand  when  rubbed  in 
the  hand  will  not  leave  fine  particles  adhering  to  it,  but  should 
the  sand  not  prove  to  be  clean,  the  character  of  the  impurities 
should  be  investigated  before  finally  rejecting  it.     When  there 
is  not  time  for  making  proper  tests,  it  will,  of  course,  be  safest 
to  use  only  such  sand  as  has  no  foreign  matter  whatever;  but 
when  strictly  pure  sand  can  only  be  obtained  at  great  cost,  tests 
may  show  that  a  small  percentage  of  impurities  may  be  tolerated. 


1  IMPURITIES  169 

Another  simple  test,  beside  the  one  of  rubbing  in  the  hand, 
is  to  place  a  little  of  the  sand  in  a  test  tube  filled  with  water; 
if  any  impurities  are  present,  they  may  separate  from  the  sand 
on  account  of  their  lighter  weight,  or  if  in  a  very  fine  state  of 
division,  the  water  may  be  rendered  murky  in  appearance. 
This  test  is  not  absolute,  however,  especially  for  calcareous 
sand,  as  the  fine  particles  of  limestone  will  give  the  murky 
appearance  to  the  water,  although  not  objectionable  except  on 
account  of  their  extreme  fineness. 

The  use  of  poor  sand  will  result  in  a  larger  proportionate 
decrease  in  strength  for  a  mortar  containing  a  large  amount 
of  sand  than  for  one  made  with  a  small  amount.  The  effect  of 
incorporating  various  foreign  substances  in  cement  mortar  is 
treated  in  Art.  49.  As  some  of  these  substances  may  occur 
in  sand,  the  article  referred  to  should  be  read  in  connection 
with  this  subject. 

266.  SAND  WASHING.  —  When  impurities  occur,  they  may 
sometimes  be  removed  by  washing,  but  such  work  must  be 
carefully  inspected  if  the  foreign  matter  be  of  a  really  danger- 
ous character. 

In  the  construction  of  the  Canal  at  the  Cascades,  Columbia 
River,  Oregon,  quite  an  elaborate  concrete  plant  was  estab- 
lished, which  had  in  connection  a  sand  and  gravel  washer  and 
separator.1  This  consisted  of  a  tube  about  two  and  one-half 
feet  in  diameter  and  seventeen  feet  long,  made  of  one-quarter- 
inch  boiler  iron  and  revolving  about  an  axis  slightly  inclined  to 
the  horizontal.  Angle  irons  were  riveted  on  the  inside  of  the 
tube  to  carry  the  material  up  on  the  side  and  drop  it  again, 
while  a  spray  of  water  issued  from  a  perforated  pipe  inside  the 
tube.  The  materials  were  separated  by  screens  near  the  lower 
end  of  the  tube.  The  material  contained  considerable  earthy 
matter  and  is  said  to  have  been  fairly  well  washed  by  this  pro- 
cess. 

Another  style  of  sand  washer  was  designed  by  the  contract- 
ors for  the  construction  of  Lock  No.  3,  improvement  of  Alle- 
ghany  River.2  The  sand  contained  earthy  matter  and  some 
coal,  the  latter  being  hard  to  remove  by  ordinary  processes.  A 
— . * 

1  Report  of  Lt.  Edw.  Burr,  Report  Chief  of  Engineers,  1891,  p.  3334. 
2\V.  H.  Rober,  Engineering  News,  Feb.  16,  1899. 


170  CEMENT  AND  CONCRETE 

large  barrel  or  tank,  nine  feet  in  diameter  and  seven  feet  high, 
was  provided  with  double  floor,  the  upper  one  being  pierced 
with  one-inch  holes.  Paddles  were  attached  to  a  vertical  shaft 
in  the  axis  of  ^he  tank  and  revolved  by  suitable  gearing,  while 
water  was  forced  into  the  space  between  the  two  floors.  The 
water  finding  its  way  through  the  holes  in  the  upper  floor,  passed 
up  through  the  sand  and  overflowed  at  the  top,  carrying  with 
it  the  coal  and  sediment.  The  cost  of  washing  is  said  to  have 
been  about  seven  cents  per  cubic  yard,  but  it  is  evident  that 
methods  of  handling  would  have  to  be  quite  perfect  to  keep  the 
cost  at  so  low  a  figure. 

ART.  33.     CONCLUSIONS.     WEIGHT.     COST 

267.  REQUIREMENTS  FOR  GOOD  SAND.  —  In  conclusion,  then, 
we  may  say  that  good  sand  may  consist  of  grains  of  almost 
any  moderately  hard  rock  that  is  not  liable  to  future  alteration 
in  the  work.     The  grains  may  be  of  any  shape,  but  preferably 
should  be  sharp  and  angular  or  lenticular  in  form,  not  rounded 
and  smooth.     The  sand  should  not  contain  such  impurities  as 
loam  or  humus,  but  for  most  purposes  a  small  percentage  of 
clay  or  fine  rock  dust  is  not  objectionable.     Clay  should  not, 
however,  be  permitted  in  sand  for  use  in  sea  water. 

Coarse  grained  sands  are  better  than  fine  grained  ones,  but 
a  mixture  of  fine  and  coarse  is  excellent,  especially  where  but 
a  small  amount  of  cement  is  used,  because  such  a  mixture  con- 
tains less  voids  and  will  make  a  less  permeable  mortar,  while  giv- 
ing a  good  strength.  As  might  be  expected,  the  deleterious  effect 
of  poor  sand  is  more  apparent  the  larger  the  dose  of  sand  used. 

268.  Weight  of  Sand.  —  It  is  evident  from  what  has  pre- 
ceded that  the  weight  of  sand  per  cubic  foot  will  vary  greatly, 
not  only  with  the  character  of  the  rock  from  which  it  came, 
but  also  with  its  physical  condition.     Natural  sand,  as  it  or- 
dinarily occurs,  will  weigh  about  as  follows,  according  to  its 
condition :  — 

Moist  and  loose „    .    .    .       70  to  90    pounds  per  ru.  ft. 

Moist  and  shaken 75  to  100      " 

Dry  and  loose 75  to  105      " 

Dry  and  shaken 90  to  125      "  " 

When  settled  in  water,  weight  of  wet 

sand,  voids  full  ....""....  100  to  140      "  " 


. 
WEIGHT  AND  COST  171 

If  the  rock  from  which  the  sand  is  made  weighs,  say,  one 
hundred  sixty  pounds  per  cubic  foot  solid  (specific  gravity, 
2.56),  then  the  sand  will  weigh  per  cubic  foot  120,  100,  and 
80  pounds,  for  voids  of  25,  37.5  and  50  per  cent.,  respectively. 

269.  Cost  of  Sand.  —  The  cost  of  sand  will,  of  course,  vary 
with  the  locality.  In  exceptional  cases  where  it  is  found  di- 
rectly at  the  works,  it  may  not  cost  more  than  twenty  to  thirty 
cents  per  cubic  yard  to  deliver  it  on  the  mixing  platform.  If 
it  has  to  be  pumped  from  the  bed  of  a  river  or  lake  and  can  be 
conveyed  to  the  work  in  scows  with  a  tow  of  not  more  than 
ten  miles,  it  may  be  delivered  at  the  work  for  from  forty  to 
sixty  cents  per  cubic  yard.  If  it  must  be  hauled  in  wagons  for 
some  distance,  it  may  cost  from  fifty  cents  to  one  dollar  per 
yard;  and  again,  if  sand  is  so  difficult  to  obtain  that  it  must  be 
made  by  crushing  rock,  it  may  cost  from  one  dollar  to  three 
dollars  per  yard.  Usually  from  sixty  cents  to  a  dollar  is  a  fair 
price  for  sand.  Several  examples  of  cost  of  sand  will  be  given 
in  connection  with  the  subject  of  cost  of  concrete. 


CHAPTER  XII 

MORTAR:  MAKING  AND  COST 
ART.  34.     PROPORTIONS  OF  THE  INGREDIENTS 

270.  CAPACITY  OF  CEMENT  BARRELS.  —  Since  there  i*   no 
standard  size  for  cement  barrels,  the  capacities  vary  consider- 
ably, Portland  cement  barrels  ranging  from  3.1  to  3.6  cu.  ft.,  while 
natural  cement  barrels  contain  from  3.4  to  3.8  cu.  ft.     In  Ger- 
many   cement   is   packed   to    weigh   three    hundred    ninety-six 
pounds  per  barrel,  gross,  the  net  weight  being  about  three  hun- 
dred seventy-five  pounds.     American  Portland  usually  weighs 
four   hundred    pounds   gross    or   about   three    hundred    eighty 
pounds  net. 

In  1896  the  Boston  Transit  Commission  had  a  number  of 
measurements  made  of  the  capacity  of  Portland  cement  bar- 
rels, and  these  have  been  compiled  by  Mr.  Sanford  E.  Thompson.1 
Table  58  presents  some  of  the  averages  obtained  from  this  series 
of  tests.  It  is  seen  that  the  capacity  of  the  barrels  varied  from 
3.12  to  3.50  cu.  ft.,  the  mean  volume  being  3.29  cu.  ft.  The 
difference  between  the  capacity  of  the  barrel  and  the  volume 
of  the  packed  cement  contained  is  due  to  the  fact  that  there 
is  usually  a  small  space  beneath  the  head  not  filled  with  cement. 
A  barrel  of  packed  cement  makes  about  1.25  barrels,  measured 
loose . 

271.  Natural    cements    made    in    the    East    are    packed    to 
weigh  three  hundred  pounds  net,  while  some  of  the  Western 
natural  cements  weigh  but  two  hundred  sixty-five  pounds  per 
barrel  net.     Any  of  the  natural  cement  factories  will  doubtless 
pack  their  cement  to  suit  customers  on  large  orders,  and  there 
seems  to  be  little  reason  for  this  variation  in  weight  between 
the  West  and  the  East.     There  would  perhaps  be  some  trouble 
in  getting  three  hundred  pounds  of  a  very  light,  finely  ground, 
natural  cement  in  the  ordinary  sized  barrel,  but  two  hundred 


1  Engineering  News,  Oct.  4,  1900. 

172 


PROPORTIONS 


173 


TABLE   58 
Capacity  of  Portland  Cement  Barrels 


HIGHEST. 

LOWEST. 

MEAN. 

Height  of  barrel  between  heads,  feet     .... 
Capacity  between  heads,  cubic  feet  
Volume  of  packed  cement  in  barrel,  cubic  feet  . 
Volume  of  loose  cement  in  barrel,  cubic  feet  . 
Net  weight  of  cement  in  barrel,  pounds    . 
Weight  per  cubic  foot  of  cement  as  packed  in 
barrel    pounds 

2.19 
3.50 
3.48 
4.10 
387.0 

123  16 

2.01 
3.12 
3.03 
3.75 
370.7 

113  81 

2.00 
3.21) 
3.  IK 
4.07 
377.4 

I  ]g  79 

Weight  per  cubic  foot,  loose,  pounds     .... 

100.40 

88.r,2 

92.63 

NOTE.  —  Results  are  averages  of  thirty-one  tests  with  seven  brands,  four 
of  which  were  American.  The  above  data  compiled  by  Sanford  E.  Thomp- 
son and  published  in  Engineering  News  of  Oct.  4,  1900. 

eighty  pounds  may  be  put  in  a  barrel  without  difficulty,  and  it 
would  seem  that  a  compromise  might  be  made  on  this  weight. 

272.  QUANTITY  OF  SAND.  —  The  amount  of  sand  to  be  used 
in  mortar  will  depend  entirely  on  the  character  of  the  work 
and  the  quality  of  the  cement  and  sand.     If  it  is  merely  a 
matter  of  strength  to  be  developed,  no  special  care  need  be 
taken  to  have  the  voids  in  the  sand  filled  with  cement,  but  if 
an  impervious  mortar  is  desired,  the  mortar  must  not  be  too 
poor  in  cement,  even  though  only  a  moderate  strength  is  re- 
quired. 

In  France  the  proportions  of  cement  and  sand  are  usually 
given  in  terms  of  kilograms  of  cement  to  one  cubic  meter  of 
sand.  In  England  and  America  the  proportions  are  usually 
given  by  volume,  as  so  many  parts  of  cement  to  one  of  sand, 
while  in  Germany  the  proportions  are  given  by  weight.  The 
bulk  of  cement  varies  so  much  according  to  the  degree  of  pack- 
ing, and  the  volume  of  sand  is  so  varied  by  the  amount  of  mois- 
ture contained,  that  the  German  method  of  stating  proportions 
by  weight  seems  to  be  the  most  logical  one  to  adopt. 

273.  Proportions  by  Volume.  —  It  has  been  shown  that  the 
volume  of   a  given  quantity  of  cement  may  vary  twenty-five 
per  cent,  according  as  it  is  measured  packed  or  loose,  and  that 
likewise  the  volume  of  sand  may  vary  twenty  per  cent,  accord- 
ing to  the  amount  of   moisture  contained.     This  makes  it  ne- 
cessary to  take  great  precaution  in  proportioning   mortars   by 


174  CEMENT  AND  CONCRETE 

volume  if  the  desired  richness  of  the  mortar  is  to  be  assured. 
Nevertheless,  mortars  for  use  in  actual  construction  are  usually 
proportioned  by  volume.  The  usual  method  is  to  taste  the 
proportions  as  one  part  of  packed  cement  (as  it  comes  in  the 
barrel  or  bag)  to  so  many  parts  of  loose  sand,  but  proportions 
are  sometimes  stated  as  volumes  of  loose  sand  to  one  volume 
of  loose  cement. 

274.  Equivalent  Proportions  by  Weight  and  Volume.  —  As 
cement  is  now  so  frequently  sold  in  sacks  of  one-fourth  barrel 
each,  in  which  the  cement  is  not  so  compact  as  in  a  barrel,  we 
have  assumed  the  contents  of  a  barrel  to  be  3.45  cu.  ft.  for 
Portland,   and   3.75   cu.   ft.   for   natural,   which   are   somewhat 
higher   than   the    mean   actual    capacities   of   stave   barrels   as 
shown   by   tests.     At   three   hundred   eighty   pounds   and   two 
hundred   eighty   pounds   net   weight  respectively  for   Portland 
and  natural,  this  is  equivalent  to  one  hundred  ten  pounds  per 
cubic  foot  and  seventy-five  pounds  per  cubic  foot   packed.     If 
we  also  assume  that  loose  cement  weighs  eighty-five  pounds  per 
cubic  foot  for  Portland    and  sixty  pounds  per  cubic  foot  for 
natural;  and  that  loose,  dry  sand  weighs  one  hundred  pounds 
per  cubic  foot,  while  loose,  damp  sand  weighs  eighty  pounds  per 
cubic  foot,  we  may  obtain  the  following  comparisons,  Table  59. 

275.  It  is  evident  that  in  all  specifications  and  in  reports 
of  tests,  as  well  as  in  the  use  of  cement,  the  method  of  stating 
proportions  should  be  made  clear,  and  in  interpreting  the  re- 
sults of  tests  this  must  be  borne  in  mind.     For  instance,  in 
tests  to  compare  the  value  of  limestone  screenings  with  quartz 
sand,  proportions  by  weight  will  favor  the  quartz,  while  pro- 
portions by  volume  will  favor  the  screenings,  since  the  latter 
are  lighter. 

276.  Richness  of  Mortar.  —  Mortars  containing  small  amounts 
of   sand   are   often   stronger   than   neat   cement   mortars.     Es- 
pecially is  this  true  of  most  natural  cements.     Some  of  these 
will  give  as  high  strengths  when  mixed  with  two  parts  sand  by 
weight  as  when  neat,  and  usually  the  one-to-one  mortars  are 
stronger  than  the  neat  mortars.     These  remarks  refer  to  tensile 
tests  where  a  good  quality  of  sand  is  used  and  the  mortars  are 
three   months   old   or   more.     The   neat   cement   mortars   gain 
their  strength  more  rapidly,  short  time  tests  usually  not  show- 
ing the  results  mentioned,     Portland  cements  of  good  quality 


PROPORTIONS 


175 


TABLE   59 


Comparison  of  Proportions  by  Weight  and  Volume 


EQUIVALENT  PARTS  SAND,  PROPORTIONS  STATED  BY  VOLUME. 

PORTLAND  CEMENT. 

NATURAL  CEMENT. 

PARTS  DRY 

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1 

1.10 

1.38 

085 

1.06 

0.75 

0.94 

0.60 

0.75 

2 

2.20 

2.75 

1.70 

2.12 

1.50 

1.88 

1.20 

1.50 

3 

3.30 

4  12 

2.55 

3.19 

2.25 

2.81 

1  80 

2.25 

4 

4.40 

5.50 

3.40 

425 

3.00 

3.75 

2.40 

3.00 

5 

5.50 

0.88 

4.25 

5.31 

3.75 

4.6J) 

3.00 

3.75 

6 

6.60 

8.25 

5.10 

6.38 

4.50 

5.62 

3.60 

4.50 

In  preparing  the  above  table  the  following  assumptions  are  made  : 


MATERIAL. 

WEIGHT 

IN  A 

BARREL. 

VOLUME 

OF   A 

BARREL. 

WEIGHT  TER  CUBIC  FOOT. 

Packed. 

Loose 
Dry. 

Loose 
Damp. 

Portland  cement  . 
Natural  cement    . 
Sand       .... 

380 

280 

3.45cu.  ft. 
3.75cu.  ft. 

110 
75 

85 
60 
100 

80' 

usually  give  about  the  same  tensile  strength  neat  and  with 
one  part  sand  by  weight.  Tests  showing  the  rate  of  decrease 
of  strength  with  added  sand  are  discussed  in  §§363  to  365. 

Portland  cements  are  usually  mixed  with  from  one  to  three 
parts  sand  by  weight,  and  natural  cements  are  mixed  with 
from  one  to  four  parts  by  weight  (or  three-fourths  part  to 
three  parts  by  measure).  For  certain  special  purposes  poorer 
mortars  are  sometimes  employed.  To  arrive  at  the  proper 
proportion  to  use  in  mortar  for  a  given  purpose,  the  tables  of 
strength  given  in  Chapter. XV  will  be  of  value. 

277.  Effect  of  Pebbles.  —  If  the  sand  contains  pebbles,  the 
proportions  should  be  considered  in  a  little  different  way. 
Suppose  we  make  a  one-to-three  mortar  with  sand  that  con- 
tains ten  per  cent,  of  pebbles.  We  have  in  reality,  then,  3  X  .90 
=  2.7  parts  of  sand  to  one  of  cement,  and  .3  part  pebbles  em- 
bedded in  this  richer  mortar.  This  point  is  of  special  signifi- 
cance in  making  concrete  from  gravel  containing  some  sand,  or 


176  CEMENT  AND  CONCRETE 

from  broken  stone  from  which  the  fine  particles  or  screenings 
have  not  been  removed.  Such  fine  particles  serve  to  weaken 
the  mortar  by  increasing  the  dose  of  sand,  while  the  pro- 
portion of  aggregate  is  diminished.  In  using  aggregates  con- 
taining some  fine  material,  then,  or  in  using  sand  containing 
pebbles  or  fine  gravel,  one  should  not  permit  himself  to  be  de- 
ceived as  to  the  actual  richness  of  the  resulting  mortar  or 
concrete. 

278.  AMOUNT  OF  WATER  FOR  MORTAR.  —  The  amount  of 

water  required  for  mortar  will  vary  with  the  proportion  of  sand 
to  cement,  the  character  and  condition  of  the  ingredients,  the 
weather,  and  the  purpose  which  the  mortar  is  to  serve.  If  the 
water  is  stated  as  such  a  percentage  of  the  combined  weight 
of  cement  and  sand,  the  amount  required  for  a  rich  mortar 
will  be  greater  than  for  a  poor  one,  since  the  cement  requires 
more  water  than  the  sand.  Fine  cement  will  require  more 
water  than  coarse;  the  same  is  true  of  sand.  Sand  from  ab- 
sorbent rock  will  require  a  larger  amount  of  water.  On  a  hot, 
dry  day,  more  water  must  be  used  to  allow  for  evaporation; 
and  again,  if  the  mortar  is  to  be  placed  in  contact  with  brick 
or  porous  stone,  the  mortar  must  be  more  moist  than  when 
used  in  connection  with  metal,  or  with  hard  rocks  such  as 
granite.  All  of  these  points  must  be  borne  in  mind  when 
determining  the  proper  consistency  for  a  given  purpose. 

279.  We  may  arrive  at  the  approximate  amount  of  water 
required   in   the   following    manner:    find    what   proportion    of 
water  is  required  for  the  neat  cement.     This  will  vary  among 
different  samples,  and  especially  between  Portland  and  natural 
cements;  the  former  requiring  twenty  to  twenty-eight  per  cent, 
of  water  (by  weight),  and  the  latter  thirty  to  forty  per  cent. 
Then  find  the  amount  of  water  required  to  bring  the  sand  alone 
to  the  consistency  of  mortar.     This  will  vary  considerably,  fine 
sand  requiring   much   more  water  than   coarse,   etc.,   as   men- 
tioned above.     Having  these  two  quantities,  we  may  find  the 
amount  of  water  required  for  a  mortar  having  any  given  pro- 
portions of  these  samples  of  cement  and  sand.     Thus,  suppose 
we  find  that  the  neat  cement  requires  twenty-five  per  cent, 
water  and  the  sand  ten  per  cent,  water  to  bring  them  to  the 
proper  consistency.     If  we  wish  to  make  a  one-to-three  mortar 
from  these  ingredients,  using  one  hundred  pounds  of  cement,  the 


MIXING  177 

required   amount   of   water   is    (100  X  .25)  +  (100  X  3  X  .10) 
=  25  +  30  =  55  pounds. 

280.  However,  it  will  usually  be   better  to  experiment  di- 
rectly upon  the  mixture  which  it  is  proposed  to  use,  and  for 
this  purpose  the  following  rule  will  be  found  of  value.     For 
ordinary  purposes,  that  amount  of  water  should  be  used  which 
for  given   weights   of   the   dry   ingredients   will   give   the   least 
volume  of  mortar  with  a  moderate  amount  of  packing.     In  the 
actual  use  of  mortars  it  is  not  practicable  to  state  that  a  cer- 
tain definite  amount  of  water  shall  always  be  used  with  given 
quantities  of  the  dry  materials.  '  It  is  the  resulting  consistency 
of  the  mortar  that  must  be  specified  and  insisted  upon,  while 
the  amount  of  water  required  to  produce  this  consistency  will 
vary  from  day  to  day  and  must  be  left  to  the  discretion  of  the 
inspector  or  foreman.     For  a  discussion  of  the  relation  of  con- 
sistency to  the  tensile  strength  of  the  mortar,  see  Art.  46. 

ART.  35.     MIXING  THE  MORTAR 

281.  Having  decided  upon  the  proportions  of   cement,  sand 
and  water,  it  remains  to  incorporate  these  into  a  plastic,  homo- 
geneous mass.     The  size  of  the  batch  should  be  so  adjusted,  if 
possible,  that  a  full  barrel  of  cement  shall  be  used,  and  for 
careful  work  the  amount  of  sand  should  be  weighed  instead  of 
measured.     Where  this  is  impracticable,  the  condition  of  the 
sand  from  day  to  day,  as  regards  the  amount  of  moisture  con- 
tained, should  be  taken  into  account  (see  §§  262  and  263). 

Mortar  is  usually  mixed  by  hand,  but  where  large  amounts 
are  to  be  used,  machine  mixers  may  profitably  be  introduced. 

282.  HAND  MIXING.  —  For  hand  mixing,  a  water  tight  plat- 
form or  shallow  box  should  be  used,  of  such  a  size  that  the  given 
batch  will  not  cover  the  bottom  more  than  four  inches  deep. 

If  the  sand  is  measured,  a  bottomless  box,  provided  with 
two  handles  at  each  end,  will  be  found  more  convenient  than 
the  bottomless  barrel  which  is  often  employed  for  this  purpose. 
When  the  sand  is  delivered  on  the  mixing  platform  in  barrows, 
the  latter  may  be  fitted  with  rectangular  boxes  to  avoid .  re- 
measuring.  A  two-wheel  cart,  the  box  of  which  may  be  in- 
verted to  discharge  the  contents  on  the  mixing  platforjn,  will 
also  be  found  very  serviceable  when  the  runway  is  suited  to 
such  a  vehicle. 


178  CEMENT  AND  CONCRETE 

The  proper  amount  of  sand  is  evenly  spread  on  the  plat- 
form, the  cement  is  then  dumped  on  top  of  the  sand  and  spread 
out  over  it  to  an  even  thickness.  With  either  hoes  or  shovels 
the  dry  materials  are  then  thoroughly  mixed,  until,  when  a 
small  amount  is  taken  in  the  hand,  it  will  appear  of  uniform 
color  throughout.  From  two  to  five  turnings  of  the  materials, 
according  to  the  expertness  of  the  workmen,  will  be  required  to 
produce  this  result.  The  dry  mixture  is  then  drawn  to  the 
edges  of  the  platform  to  form  a  ring,  and  the  requisite  amount 
of  water  is  added  at  one  time  in  the  center.  The  mixture  is 
then  gradually  incorporated  with  the  water,  and  the  mass  is 
thoroughly  worked  until  plastic  and  homogeneous.  Should  it 
be  found  that  too  little  water  has  been  used,  a  small  amount 
may  be  added  from  a  sprinkling  pot  or  rose  nozzle,  but  the 
mass  should  always  be  worked  over  again  after  such  addition. 
Four  shovels  may  be  used  at  one  platform,  but  if  the  mixing  is 
done  by  hoes,  not  more  than  two  can  be  used  to  advantage 
with  a  batch  of  ordinary  size. 

Some  engineers  prefer  one  method  and  some  the  other,  but 
in  whatever  manner  done,  the  mixing  should  not  be  stinted. 
From  two  to  four  turnings  of  the  mass  are  usually  considered 
sufficient,  but  as  a  general  rule  it  will  be  found  that  further 
mixing,  beyond  that  required  to  just  give  the  mass  a  uniform 
appearance,  will  be  amply  repaid  in  the  strength  of  the  result- 
ing mortar.  (See  Art.  47.) 

283.  MACHINE  MIXING.  —  Where  large  quantities  of  mortar 
are  required,  machine  mixers  are  sometimes  used.  A  very 
complete  plant  for  mortar-making  was  used  in  building  the 
Titicus  Dam.1  In  this  case  machinery  was  used  in  measuring 
the  proportions  of  cement  and  sand  as  well  as  in  making  the 
mortar.  The  measuring  apparatus  consisted  of  two  cylindrical 
troughs,  one  for  cement  and  one  for  sand.  Each  trough  was 
divided,  by  means  of  six  radial  vanes  and  four  discs,  into  eigh- 
teen equal  compartments.  These  cylinders  revolved  in  cast 
iron  boxes  which  were  so  constructed  as  to  serve  as  hoppers 
for  filling  the  compartments.  Three  compartments  were  pre- 
sented to  the  hoppers  at  once,  and  slides  were  provided  by 
which  any  of  the  hoppers  could.be  cut  off  at  will.  The  cylin- 


Engineering  Record,  August  3,  1895. 


INGREDIENTS  REQUIRED  179 

ders  being  geared  to  the  same  pinion,  it  was  possible,  by  means 
of  the  slides,  to  make  any  desired  proportion  of  cement  and  sand 
from  neat  cement,  to  three  parts  sand  to  one  cement. 

The  mixing  machine  "consisted  essentially  of  a  semi-cylindri- 
cal wrought-iron  trough  with  extended  flaring  sides,  with  ele- 
ments slightly  inclined  to  the  horizontal,  and  in  its  axis  a  re- 
volving shaft  with  oblique  radial  blades  set  at  an  incline  of 
ninety  degrees  to  each  other  and  of  a  length  to  just  clear  the 
bottom  of  the  trough." 

284.  Another  form  of  machine  that  is  sometimes  employed 
consists  of  a  semi-cylindrical  trough  in  which  rotates  an  axis 
carrying  a  blade  in  the  form  of  a  screw.     The  materials  are 
fed  to  the  mixer  at  one  end  and  the  screw  mixes  them  while 
working  the  mass  toward  the  other  end. 

ART.  36.     COST  OF  MORTAR* 

285.  INGREDIENTS   REQUIRED    FOR    ONE    CUBIC    YARD   OF 
MORTAR. —  The  character  of  the  ingredients  used  in  making  cement 
mortar  varies  so  much  that  it  is  difficult  to  accurately  deter- 
mine the  quantities  of  materials  required  for  a  proposed  mortar 
except  by  experimenting   with  the   materials   that  are   to   be 
employed.     It  has  been  shown  that  the  weights  per  cubic  foot 
of  both  cement  and  sand  vary  greatly  according  to  the  condi- 
tions of  packing,  the  moisture,  etc.     The  percentage  of  voids 
in  the  sand  is  one  of  the  most  important  variations  affecting 
the  amount  of  mortar  made  with  certain  materials  mixed  in 
given  proportions.     The  consistency  of  the  mortar  also  has  a 
marked  effect,  and  different  cements  show  a  considerable  varia- 
tion in  the  volume  of  mortar  that  a  given  weight  will  yield. 
In  any  general  treatment  of  the  question,  then,  we  may  expect 
only  approximate  results,  and  the  tables  given  in  this  connec- 
tion must  be  considered  in  this  light. 

286.  Results  of  Experiments.  —  The  tests  from  which  Tables 
60  and  61  were  derived,  were  made  with  a  natural  sand  weigh- 
ing about  one  hundred  pounds  to  the  cubic  foot,  dry,  and  having 
about  three-eighths  of  the  bulk  voids.     The  grains  varied  in 
size  from  0.01  in.  to  0.1  in.  in  diameter  with  a  few  grains  out- 


1  Portions  of  this  article  were  contributed  to  "  Municipal  Engineering," 
and  appeared  in  that  magazine,  Feb.,  1809. 


180 


CEMENT  AND  CONCRETE 


TABLE  60 
Ingredients  Required  for  One  Cubic  Yard  of  Mortar,  Portland  Cement 
SAND  WEIGHS  ABOUT  100  LBS.  PER  CUBIC  FOOT.  VOIDS  THREE-EIGHTHS  OF  VOLUME 

Proportions  by  Volume  Dry 
Loose  Sand  to  Loose  Cement, 
Loose  Cement  Assumed  at 
85  Ibs.  per  Cu.  Ft. 

n 

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Proportions  by  Volume  Dry 
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Cement  Assumed  at  114  Ibs.  per 
Cu.  Ft.  or  380  Ibs.  per  Bbl.  of 
3.33  Cu.  Ft. 

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Proportions  by  Volume  Dry 
Loose  Sand  to  Packed  Cement, 
Packed  Cement  Assumed 
at  104  Ibs.  per  Cu.  Ft.  or  380  ibs. 
per  Bbl.  of  3.65  Cu.  Ft. 

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PROPORTIONS  BY 
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INGREDIENTS  REQUIRED 


181 


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Proportions  by  Volume  Dry 
Loose  Sand  to  Loose  Cement, 
Loose  Cement  Assumed  at 
G0#  per  Cubic  Foot. 


Proportions  by  Vol- 
ume Dry  Loose 
Sand  to  Packed  Ce- 
ment, Packed 
Cement  Assumed  at 
75#  per  Cu.  Ft.  or 
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Proportions  by 
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Sand  to  Packed 
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Assumed  at  71  # 
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265#  Net  per 


PROPORTIONS 
WEIUHT,  DRY  SAN 
CEMENT. 


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SXHVJ 


d  o  o  6 


r~  O  O  i—     '     •     ' 

^  ;o  3q  o      .      .      . 

t^  co  'N'  f-J     .     .    . 


8:0  -c  co     •     •    • 
oo  c?  c>     .    .     . 

00  CO  -N  -H'      .      .      . 


o  GO  ;r.  t-    •    •     • 

rtl   O  •*  1--       .        .        . 
00  Tt<  7<l  -^      .      .      . 


O  00  0  00  t^  0      • 
O  >O  t>«  GO  QO  O6     . 

o  o  c  o  o  o    . 


t~  t^  O  O  t^  O      • 

Tt<  1-1  t~-  O  O  CO      . 

i-'  "*<'  c<i  <M'  -«'  -H    . 


o  o  o  o 


CO  -^  C^  (^  r-l       .       . 


O  O  O  O  O     •     ' 

-*  1-1  X  t—  »O 

n  r«  i^  o  •<*    ' 


§1-1  X  0  OS      •      • 
_  to  i—  x  x    .    . 


O  O  CO  •«* 

t<Tt<xo 

x  •«$<  n  r* 


s 


o  o  o  o 

Tt<  OC  0  Tt 


§1—  '  'M  O  Tf  t^-  ^ 
_  o  r--  x  x  x  x 


-^  co  oi  i-<  r-J  i-J 


§70  O  t-  CC  X  CO 
OS  ^  "O  C:  ?O  •* 

x'  ^'  co  c<i  ?i  ^'  ^' 


O  ^  3^  CO'*  >O 


182  CEMENT  AND  CONCRETE 

side  of  these  limits.  The  consistency  of  the  mortar  was  such 
that  when  struck  with  the  shovel  blade  the  moisture  would 
glisten  on  the  smooth  surface  thus  formed.  In  the  experiments 
the  proportions  were  determined  by  weight,  and  the  results  for 
proportions  by  volume  were  deduced  from  them.  The  results 
for  neat  natural  cement  mortar  and  for  the  natural  cement 
mortars  containing  more  than  four  parts  sand  by  weight  were 
derived  by  analogy. 

287.  Explanation  of  Tables.  —  The  first  section  of  Table  60 
gives  the  amount  of  materials  required  for  Portland   cement 
mortar  when  the  proportions  are  stated  by  weight;  the  second 
and  third  sections  refer  to  proportions  by  volume  of  loose  sand 
to  packed  cement  when  the  size  of  the  cement  barrel  is  as- 
sumed at  3.65  cu.  ft.  and  3.33  cu.  ft.,  respectively.     The  fourth 
section  gives  the  materials  required  when  the  proportions  are 
given  in  terms  of  loose  sand  to  loose  cement.     Likewise,  the 
first  section  of  Table  61  for  natural  cement  refers  to  proportions 
by  weight;  the  second,  third  and  fourth  sections,  to  propor- 
tions by  volume  of  loose  sand  to  packed   cement  when  the 
cement  weighs  265  pounds,  280  pounds  and  300  pounds,  netr 
per  barrel,  respectively;  while  the  fifth  section  refers  to  propor- 
tions of  loose  sand  to  loose  cement. 

As  has  been  shown,  the  method  of  stating  proportions  by 
weight  is  the  most  accurate,  but  when  the  sand  does  not  ap- 
proximate the  weight  of  100  pounds  per  cubic  foot  when  shoveled 
dry  into  a  measure,  the  sections  of  the  tables  referring  to  weight 
proportions  may  require  a  correction,  and  it  may  be  simpler 
to  use  the  sections  giving  proportions  by  volume  of  loose  sand 
to  packed  cement.  The  method  of  stating  proportions  by  vol- 
umes of  loose  sand  to  loose  cement  is  to  be  deprecated,  but  since 
it  is  occasionally  used,  provision  is  made  for  it  in  the  tables. 

In  using  those  portions  of  the  tables  where  the  proportions 
are  stated  by  volume,  it  should  be  borne  in  mind  that  if  the 
sand  is  damp  when  used  it  will  weigh  less  per  cubic  foot,  and 
hence  more,  by  measure,  will  be  required  to  make  a  cubic  yard 
of  mortar. 

288.  Estimating  Cost  of  Mortar.  — With  the  data  given  in 
Tables  60  and  61  and  a  knowledge  of  unit  prices  of  the  mate- 
rials used  in  the  mortar,  one  may  estimate  the  cost  of  the  ma- 
terials in  a  given  quantity  of  mortar.     The  cost  of  the  mixing 


COST  OF  MORTAR 


183 


will,  of  course,  depend  upon  the  cost  of  labor,  the  method  em- 
ployed, etc.,  and  may  vary  from  fifty  cents  to  a  dollar  and 
fifty  cents  per  cubic  yard.  If  we  assume,  for  illustration,  that 
natural  cement  can  be  delivered  on  the  mixing  platform  for 
$1.10  per  barrel  of  280  pounds  net,  that  sand  costs  60  cents 
per  cubic  yard,  and  the  mixing  costs  $1.00  per  yard  of  mortar, 
then  we  have  for  the  cost  of  a  mortar  composed  of  one  part 
cement  to  two  parts  sand  by  weight:  - 

3.46  bbls.  cement  at  $1.10 $3.80 

0.72  cu.  yd.  dry  sand  at  .60 43 

Cost  of  mixing  per  cu.  yd 1.00 

Total  cost  of  one  cu.  yd.  of  mortar $5.23 

289.  For  approximate  results,  Tables  62  and  63  give  the 
cost  of  the  materials  used  in  a  cubic  yard  of  mortar  for  different 
prices  of  cement.  In  Table  62  the  proportions  by  weight  only 
are  indicated,  since  for  Portland  the  proportions  by  volume  of 
loose  sand  to  packed  cement  vary  so  little  from  proportions 
by  weight. 

TABLE   62 
Cost  of  Portland  Cement  Mortar 

COST  OF   CEMENT    AND    SAND    IN  ONE    CUBIC    YARD   OK    PORTLAND   CEMENT 
MORTAR.     SAND,  75  CENTS  PER  Criuc  YARD 


COST  OF  PORT- 
LAND 
CEMENT  PER 
BARREL 
OF  380  POUNDS 
NET. 

COST  OF  INGREDIENTS  IN  MORTAR,  IN  DOLLARS. 
Proportions  in  Mortar  by  Weight,  —  Parts  Sand  to  One  of  Cement. 

0 

l 

2 

3 

4 

5 

6 

$1.20 

8.90 

5.33 

3.89 

3.03 

2.56 

2.23 

2.02 

1.30 

9.62 

5.73 

4.17 

3.23 

2.72 

2.36 

2.13 

1.40 

10.36 

6.14 

4.44 

3.43 

2.88 

2.49 

2.24 

1.60 

11.10 

6.55 

4.72 

3.63 

3.03 

262 

2.35 

1.60 

11.84 

6.96 

5.00 

3.83 

3.19 

2.75 

2.46 

1.70 

12.58 

7.37 

5.27 

4.03 

3.35 

2.88 

2.57 

1.80 

13.32 

7.77 

5.55 

4.23 

3.51 

3.01 

2.68 

190 

14.06 

8.18 

5.82 

4.43 

3.67 

3.13 

2.79 

2.00 

14.80 

8.59 

6.10 

4.63 

3.82 

3.26 

2.90 

2.10 

15.54 

9.00 

6.38 

4.83 

3.98 

3.39 

3.01 

2.20 

16.28 

9.41 

6.65 

5.03 

4.14 

3.52 

3.12 

2.30 

17.02 

9.81 

6.93 

5.23 

4.30 

3.65 

3.23 

2.40 

17.76 

10.22 

7.20 

5.43 

4.46 

3.78 

3.34 

2.50 

18.50 

10.63 

7.48 

5.63 

4.61 

3.91 

3.45 

2.60 

19.24 

11.04 

7.76 

5.83 

4.77 

4.04 

3.56 

2.70 

19.98 

11.45 

8.03 

6.03 

4.93 

4.17 

3.67 

2.80 

20.72 

11.85 

8.31 

6.23 

5.09 

4.30 

3.78 

2.90 

21.46 

12.26 

8.58 

6.43 

5.25 

4.42 

3.89 

3.00 

2220 

12.67 

8.86 

6.63 

5.40 

4.55 

4.00 

184 


CEMENT  AND  CONCRETE 


TABLE  63 
Cost  of  Natural  Cement  Mortar 

COST    or    CEMENT    AND   SAND    IN    ONE    CUBIC    YARD  OF   NATURAL    CEMENT 
MORTAR.     SAND,    75  CENTS   PER   CUBIC    YARD 


METHOD  OF  STATING 
PROPORTIONS,  AND 
WEIGHT  OF  CEMENT  IN 
ONE  BARREL. 

BTS  SAND  TO! 
F  CEMENT.  | 

COST  OF  CEMENT  PER  BARREL,  DOLLARS. 

fc- 

0.60 

0.70 

0.80 

0.90 

1.00 

1.10 

1.20 

1.30 

1.40 

1.50 

0 

5.07 

5.92 

6.76 

7.60 

8.45 

9.30 

10.14 

10.98 

11.83 

12.68 

1 

3.50 

4.02 

4.54 

5.06 

5.59 

6.11 

6.63 

7.15 

7.67 

8.19 

2 

2.74 

3.10 

3.47 

3.83 

4.20 

4.57 

4.93 

5.30 

5.66 

6.03 

3 

2.23 

2.50 

2.78 

3.05 

3.32 

3.59 

3.86 

4.14 

4.41 

4.68 

4, 

1.90 

2.12 

2.33 

2.54 

2.76 

2.98 

3.19 

3.41 

3.62 

3.83 

0 

4.48 

5.23 

5.98 

6.72 

7.47 

8.22 

8.96 

9.71 

10.46 

11.20 

1 

3.14 

3.60 

4.06 

4.52 

4.98 

5.44 

5,90 

6.36 

6.82 

7.28 

2 
3 

2.48 
2.04 

2.80 
2.28 

3.12 
2.52 

3.45 
2  76 

3.77 
3.00 

4.09 
3.24 

4.42 
3.48 

4.74 
3.72 

5.06 
3.96 

5.38 
4.20 

. 

4 

1.75 

1.94 

2.13 

2.32 

2.51 

2.70 

2.89 

3.08 

3.27 

3.46 

By  volume  ;    parts  dry  I 
loose  sand  to  packed  1 

0 
1 

5.07 
3.13 

5.92 
3.58 

6.76 
4.02 

7.60 
4.46 

8.45 
4.91 

9.30 
5.36 

10.14 

5.80 

10.98 
6.24 

11.83 
6.69 

12.68 
7.14 

cement.    Cement    as-J 

2 

2.29 

2.57 

2.85 

3.14 

3.42 

3.70 

3.99 

4.27 

4.55 

4.84 

sumed  265  Ibs.  per  bbl. 

3 

1.83 

2.04 

2.24 

2.45 

2.65 

2.86 

3.06 

3.26 

3.47 

3.67 

of  3.75  cu.  ft. 

4 

1.63 

1.79 

1.95 

2.11 

2.27 

2.43 

2.59 

2.75 

2.91 

3.07 

By  volume;    parts  dry  ( 

1 

2.94 

3,36 

3.77 

4.19 

4.61 

5.03 

544 

5.86 

6.28 

6.70 

loose  sand  to  packed  1 
cement.     Cement    as—  { 
sumed  300  Ibs.  per  bbl. 

2 
3 

2.22 
1.82 

2.50 
2.02 

2.77 
2.22 

3.05 
2.42 

3.32 
2.62 

360 
2.82 

3.87 
3.02 

4.15 
3.22 

4.42 
3.42 

4.70 
3.60 

of  3.75  cu.  ft.                   t 

4 

1.59 

1.75 

1.91 

2.06 

2.22 

2.38 

2.53 

2.69 

2.85 

3.00 

In  Table  63  the  cost  of  materials  in  one  cubic  yard  of  natural 
cement  mortar  is  given,  1st,  for  various  parts  of  sand  to  one 
of  cement  by  weight  when  the  cost  of  cement  refers  to  a  barrel 
of  265  pounds;  2d,  when  this  cost  is  for  a  barrel  of  300  pounds 
net;  3d,  for  various  parts  sand  to  one  cement  when  the  propor- 
tions are  expressed  as  parts  by  volume,  dry  loose  sand  to  one 
volume  of  packed  cement  weighing  265  pounds  per  barrel;  and 
4th,  when  the  proportions  are  expressed  as  parts  of  dry  loose 
sand  to  one  volume  of  packed  cement  weighing  300  pounds  per 
barrel.  The  quantities  in  the  table  are  based  upon  the  as- 
sumption that  the  sand  used  is  similar  to  that  used  in  the  ex- 
periments from  which  Tables  60  and  61  were  derived,  and  that 
the  cost  of  sand  is  seventy-five  cents  per  cubic  yard. 


!     COST  OF  MORTAR  185 

290.  Example.  —  To  indicate  the  use  of  these  tables,  let  us 
determine  the  cost  per  cubic  yard  of  natural  cement  mortar 
composed  of  one  volume  of  packed  cement  to  three  volumes  of 
loose  dry  sand  when  the  cement  weighs  300  pounds  per  barrel, 
net,  and  costs  $1.25  per  barrel,  while  sand  costs  $1.00  per  cubic 
yard.  In  the  fourth  section  of  Table  63,  opposite  three  parts 
sand  and  under  $1.20  and  $1.30,  we  find,  respectively,  $3.02  and 
$3.22;  then  with  cement  costing  $1.25  and  sand  $0.75,  we  should 
have  cost  of  mortar  per  cubic  yard  $3.12.  But  in  our  example 
sand  is  assumed  to  cost  $1.00  per  cubic  yard,  or  twenty-five 
cents  more  than  the  price  for  which  the  tables  are  computed, 
and  from  Table  61  we  find  that  for  this  mortar  0.83  cubic  yard 
of  sand  is  required.  We  must  therefore  add  to  $3.12,  .83  X  25 
=  21  cents,  giving  $3.33  as  cost  of  materials  in  one  cubic  yard 
of  the  mortar.  The  cost  of  mixing  the  mortar  must  be  added 
to  obtain  the  total  cost  per  cubic  yard. 


CHAPTER  XIII 

CONCRETE :   AGGREGATE 

291.  Cement  concrete  is  composed  of  a  mixture  of  cement 
mortar  and  fragments  of  stone,  brick  or  other  moderately  hard 
substances  to  which  the  mortar  may  adhere.     Put  in  place  while 
plastic,  it  soon  obtains  a  strength  and  hardness  equal  to  good 
building  stone.     This   property,   combined   with  its   cheapness 
and  adaptability  to  monolithic  construction,  renders  it  one  of 
the  most  useful  of  engineering  materials. 

ART.  37.     CHARACTER  OF  AGGREGATE 

292.  MATERIAL  FOR  AGGREGATE.  —  Many  of  the  points  men- 
tioned concerning  the  selection  of  a  good  sand  are  also  applicable 
to   broken  stone.     The  latter   may   be   produced   from   almost 
any  moderately  hard  rock,  provided  it  is  not  subject  to  decay. 
The  best  material  for  broken  stone  is  a  rather  hard  and  tough 
rock,  which  breaks  into  angular  fragments  with  surfaces  that 
are  not  too  smooth. 

Gravel  makes  a  good  aggregate,  although  its  surfaces  are  too 
smooth  and  rounding  to  give  the  best  results.  Coarse  gravel 
may  be  improved  by  running  it  through  a  rock  crusher  to  render 
some  of  the  fragments  angular  and  rough.  A  mixture  of  gravel 
and  broken  stone  gives  excellent  results  (see  §  454).  The  gravel 
assists  the  compacting  of  the  mass,  and  the  fragments  of  broken 
stone  furnish  a  good  bond.  A  mixture  of  this  kind  also  leaves 
but  a  small  percentage  of  voids  in  the  mass,  and  this  decreases 
the  amount  of  mortar  required. 

293.  Sandstones  are  sometimes  said  to  be  better  than  lime- 
stones,  but   this   will   depend   on   their   relative   hardness   and 
structure,  and  the  use  to  which  the  concrete  is  to  be  put;  no 
general  rule  will  apply.     Some  limestones  seem  to  be  particu- 
larly adapted  to  concrete-making,  as  the  cement  adheres  to  the 
surface  so  firmly.     Granite,  syanite  and  trap  are  excellent  for 
the   purpose.     Fragments   of   brick   and   of   other   burnt    clay 

186 


CHARACTER  OF  AGGREGATE  187 

products  give  good  results  up  to  the  limit  of  the  strength  of  the 
pieces,  but  this  limit  is  not  high.  Table  155  gives  the  results 
of  transverse  tests  of  concrete  bars  made  under  the  author's 
direction,  to  show  the  comparative  value  of  different  kinds  of 
stone.  The  results  of  these  tests  are  discussed  in  §  454. 

Mr.  E.  L.  Ransome l  has  pointed  out  that  "for  fireproof 
work,  care  should  be  taken  to  avoid  such  aggregates  as  contain 
feldspar,"  and  that  limestone  should  not  be  used  if  the  con- 
crete is  likely  to  be  subjected  to  a  long  continued  red  heat. 
The  same  writer  mentions  the  fact  that  finely  crushed  granite 
may  be  inferior  to  finely  crushed  limestone  for  use  in  concrete; 
one  reason  for  this  being  that,  "  owing  to  the  brittle  quality  of 
granite,  in  crushing  it  is  not  only  broken  into  small  pieces,  but 
many  of  these  pieces  are  so  bruised  or  contused  that  upon  a 
little  pressure  being  exerted  upon  them,  such,  for  instance,  as 
can  be  applied  by  the  finger  or  thumb,  they  will  crumble." 

294.  The  care  required  in  the  selection  of  a  proper  quality 
of  broken  stone  or  gravel  will  depend  upon  the  required  strength 
of  the  concrete.     If  a  strong  concrete  is  required,  rich  mortar  will 
not  be  able  to  make  up  a  deficiency  in  the  strength  of  the  stone; 
but  if  a  low  strength  is  sufficient,  and  consequently  a  poor  mor- 
tar is  to  be  used,  but  little  will  be  gained  by  having  a  very 
strong  rock  from  which  to  obtain  broken  stone.     In  this  case 
a  rock  which  presents  a  good  surface  to   which   mortar  may 
adhere  is  the  principal  requirement,  and  a  very  hard  rock  need 
not  be  insisted  upon. 

295.  PRESENCE  OF  SCREENINGS  IN  BROKEN  STONE.  —  it  is 
frequently  required  that  the  broken  stone  shall  be  freed  from 
all  fine  material,  resulting  from  the  crushing  of  the  stone,  before 
the  mortar  is  added  to  form  concrete.     The  wisdom  of  this 
requirement  is  not  always  clear  and  depends  upon  the  kind  of 
stone.     It  has  already  been  stated  that  some  forms  of  crusher 
dust  or  screenings  give,  if  not  too  fine,  most  excellent  results 
in  mortar;  this  is  especially  true  of  limestone  screenings.     Again, 
to  retain  in  the  broken  stone  all  of  the  screenings,  will  result  in 
diminishing  the  percentage  of  voids  in  the  aggregate,  and  thus 
decrease  the  amount  of  mortar  necessary. 

On    the  other  hand,  if  a  stone  is  covered  with  a  layer  of 


Engineering  Record,  Nov.  17,  1894. 


188  CEMENT  AND  CONCRETE 

moistened,  floury  dust,  it  cannot  be  so  readily  brought  in  direct 
contact  with  the  mortar,  and  if  the  mortar  does  reach  the 
stone  it  is  made  less  rich  by  the  dust,  which  acts  as  so  much 
fine  sand.  It  must  be  said,  however,  that  so  far  as  our  ex- 
periments go,  they  do  not  confirm  this  latter  theory  when  a 
moderate  amount  of  fine  material  is  in  question,  especially  with 
crushed  limestone.  There  is  a  reason,  however,  in  some  cases 
why  the  very  fine  material  which  acts  as  sand  should  be  screened 
out  of  broken  stone,  even  if  it  is  again  used  in  the  mortar  for 
the  concrete;  the  fine  material  collects  in  certain  parts  of  the 
bin  or  pile,  making  the  proportions  irregular,  so  that  one  batch 
of  concrete  may  have  a  rich  mortar  with  a  comparatively  large 
amount  of  stone,  while  another  may  have  a  poor  mortar  with 
but  little  stone.  If,  therefore,  all  of  that  portion  of  the  broken 
stone  finer  than,  say,  one-eighth  of  an  inch,  be  screened  out 
and  used  as  so  much  sand  in  making  the  mortar,  the  resulting 
concrete  will  be  better  and  more  nearly  uniform  in  quality. 

296.  Impurities.  —  Material   that    is   really  foreign,  such   as 
vegetable  mold  or  loam,  will  be  detrimental  to  the  strength  of 
the  concrete.     Even  clay  is  not  permissible  here  if  it  adheres  to 
the  stone,  because  if  the  surface  of  a  piece  of  stone  is  smeared 
with  clay,  the  mortar  will  not  be  able  to  adhere  as  well  to  that 
surface.     Clay  in   a   granulated   form  and  not  adhering  to  the 
stone   may  be   permitted,  however,  in  small  amounts,  possibly 
as  much  as  ten  per  cent.,  without  seriously  injuring  the  concrete 
for  many  uses. 

When  old  masonry  is  torn  down,  the  stones  are  sometimes 
crushed  for  use  in  concrete,  but  such  stones,  having  particles 
of  mortar  adhering  to  the  surfaces,  will  not  be  of  first  quality 
for  the  purpose;  their  cheapness,  however,  will  frequently  out- 
weigh such  objections. 

ART.    38.     SIZE    AND    SHAPE    OF    THE    FRAGMENTS    AND    THE 
VOLUME  OF  VOIDS 

297.  As  in  the  case  of  sand,  the  shape  of  the  fragments  and 
the  degree  of  uniformity  in  size  have  an  important  effect  on 
the  proportion  of  voids  in  the  mass,  and  all  of  these  elements 
affect  the  value  of  broken  stone  for  use  in  concrete.     As   in 
mortar  each  grain  of  sand  should  be  completely  covered  with 
cement,  so  in  concrete  should  each  piece  of  stone  be  completely 


SIZE   OF   FRAGMENTS 


189 


covered  with  mortar.  As  the  pieces  in  a  given  volume  of  broken 
stone  will  have  a  smaller  total  superficial  area  when  the  frag- 
ments are  large  than  when  they  are  small,  we  should  conclude 
that  the  larger  fragments  will  require  less  mortar  or  be  more 
thoroughly  coated  with  a  limited  amount.  From  the  same  point 
of  view  we  should  expect  that  round  fragments  would  require 
less  mortar  than  those  of  irregular  shape. 

It  is  found  however,  in  practice,  that  these  theoretical  con- 
siderations   must    be  modified    to    correspond    with    the   facts. 

TABLE   64 

Voids  in  Broken  Stone  and  Gravel  Varying  in  Granulometric 

Composition 


WEWIIT  OK 

CHARACTER  STONE. 

GR  AN  ULOMETRIC  COMPOSITION. 

BROKEN 
STONE,  LBS. 

PER 

PER  CENT. 
VOIDS. 

• 

Cu.  FT. 

Limestone     .     .     . 

K 
V 

83 
89 

47 
44 

F 

90 

43 

M 

91 

42 

C 

85 

46 

F»,  M*> 

91 

42 

F»    C*° 

94 

40 

K*>,  F»,  M&° 

102 

35£ 

K«>,  V20,  F20,  M*\  C20 

104 

34 

C,  120i  Ibs.,  K,  33*  Ibs. 

11H 

29 

Potsdam  sandstone 

V 

86 

45 

u 

M 

84 

44 

(( 

V33,  F67 

88 

43 

u 

V83,  F83,  M88 

92 

40 

(( 

K25,  V25,  F26,  M25 

97$ 

36^ 

Gravel      .... 

V 

110 

32 

t 

F 

108 

33 

i 

M 

106 

34 

c 

V«8,  F«   M88 

112 

30 

c 

V*>,  M50 

114 

29 

Potsdam  sandstone  1 

P.  6  cu.  ft.  on  £  in.    screen    ) 
G.  2  "    "  |  in.  to  Jin.  "       J 

100 

39 

and  gravel     .     .  ] 

P.  4  cu.  ft.  on  \  in.    screen    ) 
G.4  '«    "  ^in.to  Jin.  "       J 

109 

33 

NOTE  .  —  Stone  jarred  down  in  measure  for  all  trials. 
K  passed  holes  1  inch  square,  failed  to  pass  holes  TV  inch  square. 
V  "I  "  i         " 

F  "1  "  "  " 

M  "2  "  "  1          " 

C  "     3  "  "  2          " 


190 


CEMENT  AND  CONCRETE 


When  the  pieces  of  broken  stone  are  too  large,  they  do  not 
bed  themselves  well  in  the  matrix  of  mortar,  but  become  wedged 
one  against  another,  leaving  voids  in  the  concrete.  While 
round  fragments  have  a  small  superficial  area  in  relation  to 
their  volume,  have  a  small  percentage  of  voids,  and  pack  to- 
gether readily,  yet  they  are  lacking  in  ability  to  form  a  good 
bond,  and  hence  do  not  give  the  best  results. 

298.  Relation  of  Size  of  Stone  to  Volume  of  Voids.  —  As  illus- 
trating the  effect  of  the  size  of  fragments  and  granulometric  com- 
position of  stone  on  the  volume  of  voids,  Table  64  gives  a  number 
of  results  obtained  at  St.  Marys  Falls  Canal. 

Table  65  gives  some  of  the  results  obtained  by  M.  Feret  in 
similar  tests.1 

TABLE   65 
Size  of  Stone  and  Volume  of  Voids 


COMPOSITION,  BY  WEIGHT,  OF  SMALL  STONE. 

PER  CENT.  OF  VOIDS  BY  VOLUME. 

Fragments  Passing  a  Ring  of 

90  mm. 

60  mm. 

40  mm. 

20  mm. 

TJ 

and  Retained  on  a  Ring  of 

60  mm. 

40  mm. 

20  mm. 

10  mm. 

1 

0 

0 

0 

41.4 

52.1 

0 

1 

0 

0 

40.0 

53.4 

0 

0 

1 

0 

38.8 

51.7 

0 

0 

0 

1 

41.7 

52.1 

0 

1 

0 

1 

35.6 

47.1 

1 

4 

1 

1 

33.5 

48.8 

1 

1 

1 

4 

356 

46.4 

The  percentage  of  voids  in  a  mass  of  broken  stone  of  uniform 
size  should  be  independent  of  what  the  size  may  be,  and  the 
first  few  lines  in  Table  65  show  this  to  be  nearly  the  case  with 
the  four  samples  tested.  It  is  seen  from  both  tables  that  the 
more  complex  mixtures  give  smaller  percentages  of  voids,  and 
that  for  all  sizes  the  voids  are  much  less  in  the  gravel  than  in 
the  broken  stone. 


1  "  Sand  and  Stone  Used  for  Cement  Mortar  and  Concrete, "  by  M.  Feret. 
Abstracted  in  Engineering  News,  March  26,  1892. 


SIZE  OF  FRAGMENTS 


191 


299.  M.  Feret's  Experiments.  —  To  show  the  effect  of  the 
variation  in  sizes  of  fragments  on  the  strength  of  the  concrete 
made,  M.  Feret  experimented  with  four  mixtures  of  three  sizes. 
The  proportions  used  in  the  mortar  were  one  part  by  weight  of 
Portland  cement  to  three  parts  of  Boulogne  gravel,  gaged  with 
an  amount  of  water  equal  to  seventeen  per  cent,  of  the  total 
weight  of  cement  and  sand.  The  volume  of  mortar  used  in 
each  case  was  made  equal  to  the  volume  of  the  voids  in  the 
stone.  The  concrete  was  thoroughly  mixed  and  then  rammed 
into  a  large  cylindrical  mold.  After  four  months'  exposure  to 
the  air,  twelve  cubes  were  cut  from  the  cylindrical  block,  four 
cubes  being  cut  from  each  of  three  consecutive  horizontal 
layers.  These  cubes  were  placed  in  sea  water  and  crushed 
after  one  month,  being  then  five  months  old.  The  results  of 
the  tests  are  given  in  Table  66. 

TABLE    66 
Strength  of  Concrete.     Varying  Size  Stone 


MEAN  RESISTANCE  IN  KG. 

PER  SQ.  CM. 

VOL.  OF 

WEIGHT 

GRANULOMETRH; 
COMPOSITION  OF 
BROKEN  STONE. 

VOL.  OF 
VOIDS  PER 
Cu.  METER. 

MORTAR 
PER  Cu. 
MKTER  OF 

OF  CON- 
CRETE 
PER  Cu. 

OF  4  CUBES  FROM 

lid 

STONE. 

METER. 

a 

0> 

3 

Bottom. 

w  sJ2 

G 

M 

F 

Cu.  Meter. 

Cu.  Meter. 

Kg. 

4 

1 

1 

0.492 

0492 

2296 

144 

143 

173 

153 

1 

4 

1 

0.494 

0.494 

2272 

141 

141 

154 

145 

1 

1 

4 

0.486 

0.48(5 

2276 

106 

121 

133 

120 

2 

2 

2 

0.478 

0.478 

2264 

115 

132 

151 

133 

Size  "G"  of  broken  stone  passed  a  ring  60  mm.  (2.4  inches) 
in  diameter  and  was  held  by  a  ring  40  mm.  (1.6  inches)  in 
diameter;  "M"  passed  40  mm.  (1.6  inches)  ring  and  was  held 
by  a  ring  20  mm.  (0.8  inch)  in  diameter;  while  "F"  passed 
the  20  mm.  (0.8  inch)  ring  and  would  not  pass  a  ring  10  mm. 
(0.4  inch)  in  diameter. 

The  following  conclusions  are  drawn  from  this  table:  (1)  In 
each  block  the  lower  layers,  which  had  been  submitted  to 
longer  continued  ramming  than  the  upper  layers,  offered  a 


192  CEMENT  AND  CONCRETE 

greater  resistance.  (2)  The  mean  resistance  varied  according 
to  the  granulometric  composition  of  stone  used,  and  was  greater 
with  the  increasing  proportion  of  large  stone  in  each  block. 
Since  the  amount  of  mortar  used  was  in  all  cases  equal  to  the 
volume  of  voids  in  the  stone,  the  effect  of  voids  on  the  strength 
was  not  noticeable. 

300.  Further  Experiments.  —  Tables    153  and  155  give  the 
results  of  some  experiments  made  under  the  author's  direction 
to  test  the  effect  of  size  and  character  of  broken  stone.     In 
these  tests  the  proportions  are  generally  35  pounds  of  cement 
to  105  pounds  of  sand  and  3.75  cubic  feet  of  broken  stone,  the 
stone  being  measured  after  jarring  it  down  in  the  vessel.     The 
amount  of  mortar  made  was  sufficient  to  fill  the  voids  in  the 
stone  when  the  latter  did  not  exceed  about  thirty-three  per 
cent  (§§452,  454). 

It  is  seen  that,  in  general,  a  higher  result  was  given  by  mix- 
tures of  various  sizes  than  by  any  one  size  alone,  and  the  fine 
stone  gave  higher  results  than  the  coarse.  In  these  tests  the 
effect  of  voids  is  shown,  since  in  some  cases  there  was  not  suf- 
ficient mortar  to  fill  the  voids. 

301.  GRAVEL  vs.  BROKEN  STONE  AS  AGGREGATE.  —  The  ele- 
ments entering  into  the  analysis  of  the  superiority  of  one  kind 
of  aggregate  over  another  are  given  above,  but  since  the  ques- 
tion of  the  relative  merits  of  gravel  and  broken  stone  is  so 
frequently  discussed,  a  word  may  be  added  here  to  show  the 
special  points  involved  in  such  a  comparison. 

Gravel  is  composed  of  hard,  rounded  pebbles,  the  surfaces 
of  which  are  usually  quite  smooth.  On  account  of  the  manner 
of  its  formation  and  occurrence,  the  sizes  of  the  pebbles  are 
usually  graded  from  coarse  to  fine.  Occasional  beds  of  gravel 
are  found,  however,  in  which  the  sizes  of  the  several  fragments 
are  nearly  the  same.  In  broken  stone  the  fragments  are  angular 
and  usually  have  rough  surfaces,  though  the  degree  of  rough- 
ness depends  upon  the  kind  of  stone.  The  sizes  of  the  frag- 
ments as  they  come  from  the  stone  crusher  vary  from  coarse 
to  fine,  but  by  regulating  the  crusher  jaws  and  by  screening, 
any  desired  size  may  be  obtained. 

302.  In   determining   the   value   of    a   certain   material   for 
aggregate,  at  least  six  characteristics  are  to  be  considered, —  the 
strength  and  durability  of  the  stone,  the  size  and  shape  of  the 


GRAVEL  VS.  BROKEN  STONE          193 

fragments,  the  volume  of  the  voids,  and  the  character  of  the  sur- 
face to  which  the  cement  must  adhere.  As  gravel  is  usually  from 
the  igneous  rocks,  its  strength  and  durability  are  not  often  open  to 
question.  This  may  or  may  not  be  so  in  the  case  of  broken 
stone,  but  the  question  of  relative  value  of  gravel  and  broken 
stone,  which  is  so  frequently  conclusively  settled  either  one  way 
or  another,  seldom  hinges  on  this  point.  As  to  the  average  size 
of  the  fragments,  it  is  evident  that  as  a  general  proposition  it 
must  be  allowed  that  by  proper  screening  either  broken  stone 
or  gravel  may  be  obtained  of  any  desired  size. 

Of  the  three  remaining  characteristics,  the  shape  of  the 
fragments,  volume  of  voids,  and  character  of  surface,  the  first 
is  probably  the  least  important  and  the  third  of  the  greatest 
moment.  The  round  pebbles  of  the  gravel  slide  readily  one  on 
another,  and  do  not  interlock  to  give  a  good  bond.  The  angular 
fragments  of  broken  stone  give  a  better  bond,  but  on  the  other 
hand,  if  not  thoroughly  tamped,  are  likely  to  bridge,  or  arch, 
and  thus  leave  holes  in  the  mass.  On  account  of  the  shapes  of 
the  fragments  and  because  the  sizes  are  usually  more  varied  in 
gravel,  the  latter  has  generally  a  smaller  percentage  of  voids; 
thirty  to  thirty-seven  per  cent,  voids  in  gravel,  and  forty  to 
fifty  per  cent,  in  broken  stone,  may  be  considered  to  give,  in 
a  general  way,  some  comparative  figures.  Coming  now  to  the 
character  of  surface,  cement  will  not  usually  adhere  so  firmly 
to  the  smooth  surface  of  the  gravel  as  to  the  freshly  broken 
surface  of  the  fragments  of  stone,  but  this  cannot  be  con- 
sidered a  universal  rule,  for  the  strength  in  adhesion  is  not 
simply  a  matter  of  smoothness  or  roughness  as  it  appears  to 
the  eye  or  the  touch.  The  adhesion  to  limestone  may  be 
very  much  stronger  than  to  a  sandstone  which  has  a  rougher 
appearance. 

303.  Summing  up  the  relative  advantages,  we  find  that  the 
gravel  is  suitable  for  concrete  because,  first,  it  is  not  likely  to 
bridge  and  leave  holes  in  the  concrete;  if  mixed  rather  wet,  very 
little  tamping  is  required  to  compact  it;  and  second,  the  usual 
smaller  percentage  of  voids  makes  it  possible  to  secure  a  com- 
pact concrete  with  a  smaller  amount  of  mortar  than  would  be 
required  for  broken  stone.  On  the  dther  hand,  the  angular 
fragments  of  broken  stone  will  knit  together,  as  it  were,  to  form 
a  strong  concrete  if  properly  tamped,  and  the  very  important 


194  CEMENT  AND  CONCRETE 

question  of  a  suitable  surface  for  adhesion  is  usually  in  favor 
of  the  broken  stone.  It  is  evident,  then,  that  this  matter  must 
resolve  itself  into  a  question  of  relative  cost  and  suitabil- 
ity, and  a  general  statement  that  either  gravel  or  broken  stone 
is  superior,  is  not  tenable.  One  experimenter  using  a  small 
percentage  of  mortar  in  the  concrete,  so  that  the  voids  in  the 
broken  stone  are  not  nearly  filled,  may  conclude  that  gravel  is 
the  better,  while  another  experimenter  using  a  larger  amount 
of  mortar,  filling  the  voids  in  the  broken  stone  but  giving  a 
large  excess  of  mortar  for  the  gravel,  will  conclude  that  broken 
stone  is  much  to  be  preferred. 

ART.  39.     STONE  CRUSHING  AND  COST  OF  AGGREGATE 

304.  Breaking  Stone  by  Hand.  —  When  but  a  small  quantity 
of  concrete  is  to  be  made,  and  broken  stone  cannot  be  pur- 
chased in  the  vicinity,  the  stone  for  concrete  may  be  broken  by 
hand.  This  is  an  extremely  tedious  process,  however,  and  is 
generally  avoided,  since  broken  stone  prepared  in  this  way  will 
cost  from  two  dollars  and  a  half  to  four  dollars  per  cubic  yard. 
In  the  reconstruction  of  the  breakwater  at  Buffalo,  the  cost  of 
breaking  stone  by  hand  was  two  dollars  and  eighty-six  cents 
per  cubic  yard,  and  loading  on  boat  cost  thirty-nine  cents, 
making  total  cost  about  three  dollars  and  twenty-five  cents  per 
cubic  yard.1 

305.  STONE  CRUSHERS.  —  The  most  common  forms  of  rock 
crushers  are  the  gyratory  and  the  movable  jaw  types.  The 
jaw  breaker,  or  Blake  crusher,  consists  of  one  fixed  plate  or 
jaw  and  one  movable  one.  The  latter  is  hinged  at  the  upper 
end  and  the  lower  end  is  moved  backward  and  forward  through 
a  short  space  by  means  of  a  toggle  joint  or  other  mechanism. 
The  jaws  are  several  inches  apart  at  the  upper  end,  depending 
on  the  size  of  the  machine,  and  converge  toward  the  bottom. 
The  distance  between  the  jaws  at  the  bottom  regulates  the  size 
of  fragments  delivered,  and  this  distance  may  be  adjusted  at 
will. 

The  Gates  crusher  is  of  the  gyratory  type  and  consists  of 
a  corrugated  cone  of  chilled  iron,  called  the  breaking  head, 


1  Report  of  Capt.  F.  A.  Mahan  in  Report  Chief  of  Engineers,  U.S.A., 
1888,  p.  2034, 


STONE  CRUSHING  195 

wittiin  a  larger  inverted  cone,  or  shell,  which  is  lined  with  chilled 
iron  pieces.  The  vertical  shaft  bearing  the  breaking  head  is 
pivoted  at  the  upper  end  while  the  lower  end  travels  in  a  small 
circle  ;  an  eccentric  motion  is  then  imparted  to  the  head,  so  that 
it  approaches  successively  each  element  of  the  shell.  The  size  of 
opening  can  be  regulated  by  raising  or  lowering  the  breaking  head. 

Stone  crushers  are  made  of  various  sizes  having  capacities 
up  to  one  hundred  tons  per  hour.  The  cost  of  running  a  stone 
crusher  is  not  great,  the  principal  expense  being  incurred  in 
breaking  the  stone  into  pieces  of  proper  size  to  feed  the  crusher, 
the  delivery  of  the  stone  to  the  crusher,  and  taking  it  away 
when  broken. 

Crushing  plants  are  usually  provided  with  revolving  screens 
into  which  the  broken  stone  is  delivered  from  the  crusher. 
These  screens  are  usually  made  of  perforated  steel  plate, 
the  holes  being  such  as  to  separate  the  material  into  the  sizes 
desired. 

Where  large  amounts  of  concrete  are  required,  and  the  stone 
is  to  be  crushed  on  the  work,  the  arrangement  of  the  crusher 
plant  should  receive  careful  study  to  facilitate  the  transporta- 
tion of  the  rock  to  and  from  the  crusher.  The  broken  stone 
should  be  discharged  from  the  crusher  into  bins,  from  which 
the  carts  or  cars  may  be  filled  by  gravity,  or  from  which  the 
material  may  be  led  directly  to  the  mixer  through  a  chute  or 
other  form  of  conveyor.  In  quarries  preparing  aggregate  for 
sale,  and  on  important  works,  very  complete  stone  crushing 
plants  are  erected.1 

306.  COST  OF  AGGREGATE.  —  The  cost  of  aggregate  varies 
greatly  according  to  the  proximity  of  the  stone  to  the  crusher, 
the  character  of  the  stone,  and  the  amount  required.  In  ex- 
ceptional cases  gravel  suitable  for  use  in  concrete  is  so  near 
at  hand  that  it  may  be  delivered  on  the  mixing  platform  for 
from  twenty-five  to  forty  cents  per  cubic  yard.  When  it  must 
be  brought  from  a  distance,  the  cost  is  correspondingly  in- 
creased. Where  a  considerable  quantity  of  stone  is  to  be  broken, 
the  cost  of  crushing,  aside  from  transportation  of  the  materials 


1  The  stone  crushing  and  sand  and  gravel  washing  plant  used  in  the  con- 
struction of  the  Canal  at  the  Cascades  of  the  Columbia,  Ore.,  is  described 
and  illustrated  in  Report  of  Chief  of  Engineers,  1891,  p.  3332. 


196  CEMENT  AND  CONCRETE 

to  and  from  the  site  of  the  work,  would  usually  be  from  thirty 
to  forty  cents  per  cubic  yard. 

In  one  case  where  the  stone  was  delivered  to  the  crusher  in 
carts  after  having  been  sorted  from  spoil  banks  containing 
much  poor  stone  that  had  to  be  handled  over,  the  cost  per 
cubic  yard  of  crushed  stone  was  approximately  as  follows  for 
about  six  thousand  cubic  yards  crushed  in  one  season: 

Labor,  including  sorting  and  delivering  to  crusher,  per  cubic 

yard  of  crushed  stone $.67 

Rent  of  power  plant 04 

Fuel  . 05 

Tools,  supplies,  breakages,  etc 12 

Interest  and  depreciation  of  plant 12 


Total  cost  per  cubic  yard $1.00 

307.  The  following  data  concerning  the  cost  of  breaking  a 
large  amount  of  stone  for  road  material  are  given  by  Messrs. 
Spielman  and  Brush.1  "The  stone  was  broken  by  a  ten-inch 
Blake  stone  crusher  at  the  rate  of  about  twenty  cubic  yards  in 
ten  hours.  The  size  of  the  stones  as  they  came  from  the  crusher 
was:  fifty  per  cent.,  two  inches  size;  twenty-five  per  cent.,  one 
and  one-half  to  one  inch  size;  twenty-five  per  cent.,  screenings 
and  pea  dust.  The  cost  of  the  crusher,  engine,  boiler,  etc., 
set  up  complete,  was  about  twenty-five  hundred  dollars.  The 
cost  of  working  per  day  independent  of  the  original  cost  of  the 
machinery  and  interest  thereon,  and  also  independent  of  any 
royalty  on  the  stone,  was  found  by  the  contractor  to  be  as 
follows:  — 

Repairs,  lubricants,  wear  and  tear  on  crusher  and  engine,  about  $6.00 
1  engineman,  $2.50;  1  feeder,  $1.50;  1  screener,  $1.50;  5  laborers 

quarrying  and  breaking  up  stone  at  $1.00 10.50 

1  team  hauling  stone 5.00 

$  ton  coal 2.50 


Cost  of  preparing  and  crushing  20  cu.  yds.  of  stone,    $24.00 
Cost  of  one  cubic  yard,  $1.20. 

308.    The  cost  of  breaking  trap  on  the  Palisades  is  given  as 
follows:2  "Two  crushers  deliver  thirty-five  cubic  yards  of  two- 


1  Trans.  Am.  Soc.  C.  E.,  April,  1879. 

2  "Construction  and  Maintenance  of  Roads,"  by  Mr.  Edward  P.  North, 
M.  Am.  Soc.  C.  E.,  Trans.  A.  S.  C.  E.,  April  16,  1879. 


COST  OF  CRUSHING  STONE  197 

inch  stone  per  day.  when  working  well,  the  stone  being  sledged 
to  go  into  the  jaws  readily;  fifteen  per  cent,  of  the  time  is  lost 
by  breakdowns:  — 

1  engineman  and  fireman $2.50 

2  laborers  feeding,  at  $1.25 2.50 

2  laborers  screening,  at  $1.25 2.50 

Coal,  1  ton      3.50 

Oil  and  waste 1.00 

Breakages 5.00 

$17.00 
or  about  fifty-seven  cents  per  cubic  yard. 

"On  Snake  Island,  three  crushers  were  arranged  in  a  row, 
and  the  broken  stone  was  carried  by  an  endless  belt  to  the 
revolving  screen,  whence  it  fell  into  the  bins,  so  that  no  screen- 
ers  were  employed.  The  engine  had  one  cylinder,  eight  inches 
by  twenty-four  inches,  and  was  running  with  eighty  pounds  of 
steam.  The  product  was  said  to  be  one  hundred  eighty  cubic 
yards  per  day  when  there  was  no  breakdown."  The  cost  was 
as  follows:1  — 

1  engineman  and  fireman $2.50 

3  laborers  feeding,  at  $1.25 3.75 

1\  tons  coal,  at  $3.50 8.75 

Oil,  etc 2.00 

Breakages 15.00 

$32.00 

"Allowing  for  the  fifteen  per  cent,  lost  by  breakdowns,  the 
cost  would  be  about  twenty-one  cents  per  cubic  yard." 

At  another  place  on  the  Hudson,  two  crushers,  set  face  to 
face,  nine-inch  by  fifteen-inch  jaws,  could  deliver  at  the  rate  of 
one  hundred  twenty  cubic  yards  per  day  when  no  trouble 
occurred,  but  one  hundred  cubic  yards  was  a  fair  average. 

COST. 

1  engineman  and  fireman $2.50 

3  feeders 3.75 

2  screeners      2.50 

\\  tons  coal,  at  $4.00 6.00 

Oil,  etc 2.50 

Repairs 10.00 

$27.00 
or  twenty-seven  cents  per  cubic  yard." 


1  "Construction  and  Maintenance  of  Roads,"  by  Mr.  Edward  P.  North, 
M.  Am.  Soc.  C.  E.     Trans.  A.  S.  C.  E.,  April  16,  1879. 


198 


CEMENT  AND  CONCRETE 


It  is  noticeable  that  in  all  the  above  cases  the  item  for 
repairs  is  very  large.  The  wages  paid  are  lower  than  at 
present. 

309.  The  following  data  concerning  the  cost  of  quarrying 
and  crushing  about  five  thousand  six  hundred. yards  of  broken 
stone  at  Baraboo,  Wis.,  is  taken  from  an  article  by  Mr.  W.  G. 
Kirchoffer,  C.  E.1 

Cost  per  Cubic  Yard  of  Crushed  Rock 


ITEMS. 

1901. 

1902. 

Stone  in  quarry 

$   .040 

$    .027 

Dynamite,  at  24  to  27  cents  pound    . 
Tools,   repairs,    depreciation,    supplies   and 
improvements                      . 

.056 

.200 

.110 
.218 

Labor,  quarrying  and  tending  crusher    . 
Fuel,  at  §4.60  per  ton,  and  oil     .... 
Rent  of  engine   

.714 

.078 
.085 

.544 
.053 
.006 

Superintendence,  including  livery      . 

.086 
.500 

.165 
.500 

Total  cost  per  cubic  yard     . 

11.76 

$1.68 

The  cost  of  common  labor  was  fifteen  cents  an  hour,  quarry- 
men  and  drill  runners,  seventeen  and  one-half  to  twenty  cents, 
engineers  and  engine,  thirty-five  cents,  and  team  and  driver, 
thirty  cents. 

310.  The  cost  of  crushing  cobble  stone  with  a  rented  plant 
at  Port  Huron,  Mich.,  is  given  by  Mr.  Frank  F.  Rogers,  C.  E.; 
from  which  the  following  data  have  been  derived.2 


JULY  AND 
AUGUST. 

OCTOBER 

AND 

NOVEMBER. 

Hours  run                        

171.5 

94 

Stone  crushed   cubic  yards      

1145. 

522.0 

Average  cubic  yards  crushed  per  hour  .     . 
Average  rental  cost  per  cubic  yard  .     .     . 
Average  fuel  cost  per  cubic  yard  .... 
Average  labor  cost  per  cubic  yard    . 
Average  total  cost  of  crushing  per  cu.  yd. 

6.67 
11.  6  cents 
3.7    " 
22.2    " 
37.5    " 

5.55 
16.1  cents 
7.1     " 
27.9     " 
51.1     " 

1  Engineering  News,  Jan.  15,  1903. 

2  Michigan  Engineers'   Annual,    1902,   abstracted  in  Engineering  News, 


March  6,  1902. 


COST  OF  CRUSHING  STONE          199 

In  the  construction  of  the  defenses  at  Portland,  Me.,1  a  No. 
5  Champion  Crusher  was  used,  driven  by  a  thirty  horse-power 
portable  engine.  Granite  was  purchased  at  one  dollar  per  ton 
on  the  wharf.  Hauling  to  crusher  cost  thirteen  cents  per  ton. 
Cost  of  crushing,  twenty  cents  per  cubic  yard  of  crushed  stone, 
making  total  cost  of  crushed  stone  in  bin  at  crusher  one  dollar 
eighty-three  cents  per  cu.  yd. 


1  Report  of  Charles  P.  Williams;  Officer  in   charge,  Maj.  Solomon  W. 
Roessler,  Corps  of  Engineers, U.S. A.;  Report  Chief  of  Engineers,  1900,  p.  757. 


CHAPTER  XIV 

CONCRETE   MAKING:   METHODS   AND   COST 

ART.  40.     PROPORTIONS  OF  THE  INGREDIENTS1 

311.  Concrete  is  simply  a   class    of   masonry  in  which   the 
stones  are  small  and  of  irregular  shape.     The  strength  of  the 
concrete  largely  depends  upon  the  strength  of  the  mortar;  in 
fact,  this  dependence  will  be  much  closer  than  in  the  case  of 
other  classes  of  masonry,  since  it  may  be  stated  as  a  general 
rule,  that  the  larger  and  more  perfectly  cut  are  the  stone,  the 
less  will  the  strength  of  the  masonry  depend  upon  the  strength 
of  the  mortar. 

In  deciding,  then,  upon  the  proportions  of  ingredients  to  use 
in  a  given  case,  the  quality  of  the  mortar  should  first  be  con- 
sidered. If  the  concrete  is  to  be  subject  to  but  a  moderate 
compressive  stress,  the  mortar  may  be  comparatively  poor  in 
cement;  but  if  great  strength  is  required,  the  mortar  must  be 
of  sufficient  richness;  while  if  imperviousness  is  desired,  the 
mortar  must  also  possess  this  quality  and  be  sufficient  to  thor- 
oughly fill  the  voids  in  the  stone. 

312.  THEORY  OF  PROPORTIONS.  —  The  usual  method  of  stat- 
ing proportions  in  concrete  is  to  give  the  number  of  parts  of 
sand  and   aggregate  to  one  of  cement.     These   parts   usually 
refer  to  volumes  of  sand  and  stone,  measured  loose,  to  one  vol- 
ume of  packed  cement.     However,  there  is  no  established  prac- 
tice in  regard  to  this  and  a  "  1-2-5  concrete"  may  mean  five 
volumes  of  loose  stone  to  two  volumes  loose  sand  to  one  volume 
loose  cement,  or  any  one  of  several  combinations. 

This  method  of  stating  proportions  leads  to  confusion  unless 
one  is  careful  to  explain  what  is  meant  by  such  an  expres- 
sion as  "  1-3-6  concrete."  The  evils  of  similar  methods  of 
stating  proportions  in  mortars,  and  the  desirability  of  fixing 
upon  some  standard  system  of  weight  or  volume,  have  already 


1  Portions  of  this  article  were  contributed  to  Municipal  Engineering  by 
the  author,  and  appeared  in  that  magazine,  May,  1899. 

200 


PROPORTIONS  OF  THE  INGREDIENTS  201 

been  pointed  out.  The  only  circumstances  under  which  such 
expressions  as  the  above  may  be  used  with  propriety  are  when 
one  wishes  to  give  only  an  approximate  idea  of  the  character 
of  concrete  used. 

From  tests  of  strength  it  is  known  that  to  obtain  the  strong- 
est concrete  with  a  given  quality  of  mortar  the  quantity  of  the 
latter  should  be  just  sufficient  to  fill  the  voids  in  the  aggregate. 
The  strength  is  notably  diminishe  i  if  the  mortar  is  deficient, 
and  is  also  impaired  by  a  large  excess  of  mortar.  This  last 
statement  is  subject  to  one  exception:  if  the  mortar  is  stronger 
than  the  stone,  then  an  excess  of  mortar  does  not  weaken  the 
concrete.  This  case,  however,  should  never  be  allowed  to  occur, 
since  it  is  evident  that  the  strength  of  the  stone  should  be  at 
least  equal  to  the  required  strength  of  the  concrete.  Further, 
the  ordinary  uses  of  concrete  are  generally  best  served  by  a 
compact  mixture  containing  as  few  voids  as  possible. 

For  these  reasons,  then,  one  should  consider  concrete  not  as 
a  mixture  of  cement,  sand  and  stone,  but  rather  as  a  volume 
of  aggregate  bound  together  by  a  mortar  of  the  proper  strength. 
The  volume  of  voids  in  the  aggregate,  the  per  cent,  of  this 
volume  filled  with  mortar,  and  the  strength  of  this  mortar  be- 
come then  the  important  considerations  in  proportioning  con- 
crete. When  thus  considered,  it  is  an  easy  matter  to  determine 
the  required  volume  of  mortar  for  a  given  volume  of  stone, 
and  the  amount  of  cement  and  sand  required  for  a  given  volume 
of  mortar  has  already  been  considered. 

313.  Determination  of  Amount  of  Mortar  to  Use.  —  The  bulk 
of  a  given  quantity  of  broken  stone  is  not  so  variable  as  the 
volume  of  sand.  The  volume  of  the  stone,  and  consequently 
the  voids,  will  vary  with  the  degree  of  packing,  but  the  packing 
is  not  influenced  appreciably  by  the  amount  of  moisture  present. 

The  proportion  of  voids  in  the  broken  stone  may  be  obtained 
as  follows:  Find  the  weight  per  cubic  foot  of  the  broken  stone 
in  the  condition  in  which  the  volume  of  voids  is  sought,  being 
careful  to  use  a  measure  holding  not  less  than  two  or  three  cubic 
feet.  Also  obtain  the  specific  gravity,  and  hence  the  weight 
per  cubic  foot  of  the  solid  stone.  Then  one,  less  the  quotient 
obtained  by  dividing  the  weight  per  cubic  foot  of  the  broken 
stone  by  the  weight  per  cubic  foot  of  the  solid  stone,  will  be 
the  proportion  of  voids  in  the  aggregate. 


202  CEMENT  AND  CONCRETE 

For  example,  suppose  the  weight  per  cubic  foot  of  the  broken 
stone  is  102  pounds.  The  specific  gravity  of  the  solid  stone 
determined  in  the  ordinary  manner  is  found  to  be  2.724.  Then 
weight  per  cubic  foot  of  solid  stone  is  62.4  X  2.724  =170 

102 
pounds  and  1  —  -     =  .40,  voids  in  stone. 


Another  method  is  to  fill  a  vessel  of  known  capacity  with 
the.  stone  to  be  used,  and  to  pour  in  a  measured  quantity  of 
water  until  the  vessel  is  entirely  filled.  The  volume  of  water 
required  indicates  the  necessary  amount  of  mortar  to  use.  The 
stone  should  be  moistened  before  placing  in  the  vessel,  to  approxi- 
mate more  nearly  its  condition  when  used  for  concrete,  and  to 
avoid  an  error  from  absorption  of  the  waterjised  to  measure  voids. 

314.  As  to  the  degree   of  jarring  or  packing  to  which  the 
stone  should  be  subjected  in  filling  the  measure,  if  the  stone 
is  filled  in  loose,  and  it  is  proposed  to  ram  the  concrete  in  place, 
the  amount  of  mortar  indicated  will  be  a  little  more  than  the 
required  quantity.     If  the   concrete  is  to   be   placed   without 
ramming  (as  in  submarine  construction),  the  amount  of  mortar 
indicated  will  not  be  too  great.     On  the  other  hand,  if  the  stone 
is  shaken  down  in  the  vessel  to  refusal,  the  voids  obtained  will 
be  less  than  the  amount  of  mortar  which  should  be  used,  be- 
cause it  is  not  possible  to  obtain  a  perfect  distribution  of  mor- 
tar in  a  mass  of  concrete,  and  because  the  concrete  will  usually 
occupy  a  greater  space  than  did  the  stone  when  shaken  down. 
And  again,  for  perfect  concrete,  pieces  of  stone  should  be  sepa- 
rated one  from  another  by  a  thin  film  of  mortar,  and  hence  the 
volume  of  the  concrete  will  be  greater  than  the  volume  of  the 
stone   measured  in  a  compact  condition  without  mortar.     A 
deficiency  of  mortar  is  usually  more  detrimental  than  an  excess. 
It  is  safer,  therefore,  to  measure  the  voids  in  the  stone  loose, 
or  when  but  slightly  packed,  and  make  the  amount  of  mortar 
equal  to,  or  a  trifle  in  excess  of,  the  voids.  so  obtained. 

315.  Aggregates  Containing  Sand.  —  If  in  the  case  of  broken 
stone  all  of  the  fine  particles  are  used,  or  if  gravel  which  con- 
tains  a   considerable   amount  of  sand  is   employed,   then  this 
fine  material  or  sand  must  be  considered  as  forming  a  part  of 
the  mortar.     This  will  not  change  the  method  of  obtaining  the 
amount  of  mortar  required  for  such  broken  stone  or  gravel, 
but  it  will  change  the  composition  of  the  mortar  used.     Thus, 


MIXING  BY  HAND  203 

suppose  we  have  a  gravel  ten  per  cent  of  which  is  sand  (grains 
smaller  than  one-tenth  inch  in  diameter)  and  we  find  the  voids 
to  be  thirty-three  and  one-third  per  cent.  To  three  cubic  yards 
of  this  gravel  we  will  add  one  cubic  yard  of  a  one-to-three 
mortar.  The  voids  will  be  filled,  but  instead  of  having  three 
cubic  yards  of  stone  imbedded  in  one  cubic  yard  of  a  one-to- 
threc  mortar,  we  will  in  reality  have  a  little  less  than  that 
amount  of  stone  imbedded  in  a  mortar  composed  of  one  part 
of  cement  to  about  three  and  three-tenths  parts  sand. 

316.  Required  Strength.  —  In  the  paragraphs  just  preced- 
ing, an  attempt  has  been  made  to  indicate  the  general  principles 
to  be  applied  in  proportioning  the  materials  in  concrete.  To 
decide  on  the  actual  proportions  of  the  ingredients  to  use  for  a 
given  purpose,  one  must  have  clearly  in  mind  the  strength  that 
will  be  demanded  and  any  special  condition  to  which  the  con- 
crete is  to  be  subjected.  A  reference  to  Art.  57  concerning  the 
strength  of  concrete,  will  be  of  service  in  deciding  on  the  proper 
proportions  to  use  in  a  given  case. 

ART.  41.     MIXING  CONCRETE  BY  HAND 

317.  Necessity  of  Thorough  Mixing.  —  Too  much  stress  can 
hardly   be  laid  upon  the   necessity  of  thoroughly   mixing  the 
concrete  if  the  best  results  are  to  be  attained.     It  has  already 
been  shown  that  thoroughness  in  mixing  mortar  is  repaid  by 
greatly  increased  strength,  and  the  result  is  even  more  marked 
in  the  case  of  concrete.     Every  grain  of  sand  should  be  coated 
with  cement,  and  every  piece  of  stone  should  be  covered  with 
mortar.     In  general,  the  cost  of  mixing  is  from  one-tenth  to 
one-fifth  of  the  total  cost  of  the  concrete  in  place.     If  by  doub- 
ling the  cost  of  mixing  we  can  increase  its  strength  more  than 
one-tenth  or  one-fifth  in  these  respective  cases,   or  permit  a 
corresponding  decrease  in  the  amount  of  cement  necessary  for 
a  given  result,  the  additional  labor  in  mixing  is  justified. 

318.  Concrete  may  be  mixed  by  hand  or  by  machine.     Opin- 
ions vary  as  to  the  comparative  merits  of  the  two  systems,  but 
as   a   machine   properly   installed   usually   furnishes   much   the 
cheaper  method  of  mixing,  it  is  usually  employed.     The  saving 
by  this  method,  however,  will  evidently  depend  upon  the  cost 
of  labor,  the  total  amount  of  work  to  be  done,  and  the  degree 
of  concentration  of  the  work,  or  facilities  for  distributing  the 


204  CEMENT  AND  CONCRETE 

concrete.  In  certain  sections  where  cheap  labor  is  abundant, 
the  cost  of  hand  mixing  may  be  as  low  as  machine  mixing. 

With  proper  supervision,  hand  mixing  may  be  thorough,  and 
the  chief  argument  against  it,  aside  from  its  cost,  is  that  such 
hard  work  is  likely  to  be  slighted.  The  best  forms  of  mixers 
now  on  the  market,  however,  give  results  quite  equal  to  the  best 
hand  work. 

319.  METHOD  OF  HAND  MIXING.  —  We  will  assume  that  the 
materials  have  been  brought  within  easy  reach  of  the  mixing 
place.  If  the  concrete  is  to  be  mixed  near  the  point  where  it 
is  to  be  deposited,  the  mixing  platform  must  be  made  portable. 
Three  platforms,  each  8  by  14  feet,  built  of  two-inch  plank  or 
of  two  layers  of  one-inch  boards,  nailed  to  four  2x6  inch  longi- 
tudinal scantlings  laid  flat,  will  b3  suitable  for  such  a  case. 
The  platforms  should  be  made  without  vertical  sides,  though  if 
desired  a  narrow  piece  of  one-inch  board  may  be  laid  flat  around 
the  edges  and  nailed.  A  short  piece  of  rope  attached  to  each 
corner  of  the  platforms,  or  to  the  ends  of  the  longitudinal  scant- 
lings, will  be  found  convenient  in  moving  them.  These  mixing 
boards  are  placed  side  by  side. 

The  sand,  which  may  be  delivered  to  the  mixing  platform 
in  wheelbarrows,  is  first  dumped  on  the  board  and  spread 
evenly  over  the  surface.  If  the  sand  is  measured,  the  barrows 
should  be  so  arranged  as  to  hold  the  required  amount  after 
" striking"  with  a  straight  edge.  This  will  make  the  measure- 
ment independent  of  the  judgment  of  the  shoveler.  If  the  sand 
is  delivered  in  cars,  bottomless  boxes  of  two  or  three  barrels 
capacity,  according  to  the  proportions  used,  will  be  found 
more  convenient  for  measuring  than  barrels.  If  the  sand  is 
determined  by  weight,  which  as  has  been  shown  is  the  more 
accurate  method,  the  scales  should  be  set  at  a  weight  which  is 
a  factor  of  the  total  weight,  and  but  little  time  will  be  required 
to  bring  the  scales  to  a  balance  for  each  barrow. 

If  it  is  possible,  the  batch  should  be  of  such  a  size  as  to 
take  either  one  or  two  full  barrels,  or  a  certain  number  of  full 
sacks  of  cement.  This  will  obviate  the  necessity  of  measuring 
or  weighing  the  cement.  The  sand  having  been  spread  over  the 
surface  of  the  mixing  board,  the  cement  is  dumped  upon  it  and 
spread  evenly  over  the  sand.  These  ingredients  are  then  mixed 
dry,  the  required  amount  of  water  is  added  at  one  time  in  the 


i      MIXING  BY  HAND  205 

center  of  a  ring  formed  of  the  dry  materials,  and   the  whole  is 
thoroughly  mixed  as  described  under  the  head  of  mortar-making. 

320.  The  mortar  having  been  spread  evenly  over  the  board, 
the   broken  stone  is   dumped   upon  it   and  evenly   distributed 
over  the  surface.     Four  shovelers  then  mix  the  concrete.     Each 
shoveler  starts  at  a  corner  of  the  board  and  turns  each  shovel- 
ful completely  over,  casting  toward  the  end  and  spreading  the 
mortar  a  little  as  he  draws  the  shovel  toward  him.     The  two 
shovelers  at  each  end  work  toward  each  other,  and  meeting  at 
the  axis  of  the  platform,  return  to  the  side  and  repeat.     When 
the  four  shovelers  meet  at  the  center  of  the  board,  they  turn  the 
mass  again  by  casting  toward  the  center  in  a  similar  manner. 
If  in  mixing  the  concrete  it  is  found  that  sufficient  water  has 
not  been  used,  more  may  be  added  from  a  rose  nozzle,  or  sprink- 
ling pot,  previous  to  the  last  turning  of  the  mass.     The  shovel 
should  always  be  used  at  right  angles  to  either  the  side  or  the 
end  of  the  board,  never  diagonally;  and  it  should  always  scrape 
the  mass  clean  from  the  board,  never  cut  it  at  mid-depth.     From 
three  to  five  turnings  are  required  to  thoroughly  mix  the  concrete. 

The  mode  of  mixing  has  been  thus  minutely  described,  be- 
cause if  a  gang  of  men  are  started  properly  they  will  soon  be- 
come expert,  working  in  unison;  whereas  if  each  man  is  allowed 
to  mix  according  to  his  notion,  confusion  is  sure  to  result.  It 
is  sometimes  preferred  to  spread  the  stone  on  a  separate  board 
and- cast  the  mortar  upon  it,  but  this  necessitates  one  handling 
of  the  mortar  which  does  not  appear  to  contribute  much  to  the 
incorporation  of  the  ingredients. 

While  the  shovelers  are  engaged  in  mixing  the  concrete  on 
one  platform,  the  mortar  mixers  have  proceeded  to  the  next 
platform  to  mix  another  batch  of  mortar,  and  the  cement  and 
sand  are  being  placed  upon  the  third  platform.  Thus  the  work 
proceeds  in  regular  progression  without  delays.  The  shoveling 
of  concrete  is  hard  work,  and  it  will  be  found  necessary  not 
only  to  pick  good  men  for  this  duty,  but  to  cull  them  until  the 
evolution  results  in  the  proper  men  for  the  work.  An  extra 
compensation  for  men  who  perform  satisfactory  service  in  the 
mixing  of  concrete  will  usually  be  repaid  in  the  character  and 
quantity  of  the  output. 

321.  With    the    method   described   above,    a   working   gang 
would  consist  of  the  following  men  under  ordinary  conditions:  — 


206  CEMENT  AND  CONCRETE 

Measuring  and  supplying  cement  and  sand 1 

Mixing  mortar 2 

Delivering  stone  from  bin,  one  man  with  horse  and  cart,  or  two 

men  with  barrows 2 

Shovellers  to  mix  concrete  and  cast  or  wheel  to  place      ....  4 

Water  boy 1 

Spreading  and  tamping  concrete 1 

Total  men  required 11 

If  it  is  found  impracticable  to  mix  the  concrete  near  the 
place  of  deposition,  it  may  be  necessary  to  put  on  two  or  more 
extra  men  to  wheel  the  concrete  to  place.  This  gang  of  eleven 
men  may  be  doubled  and  still  work  on  the  same  three  platforms 
when  so  desired. 

With  a  moderate  length  of  wheel  for  the  materials  and  the 
finished  concrete,  a  gang  of  eleven  picked  men,  working  ac- 
cording to  system,  will  be  able  to  make  from  twenty-five  to 
thirty  cubic  yards  per  day  of  ten  hours,  or  about  two  and  a 
half  yards  per  man.  The  double  gang  of  twenty-two  men  may 
not  work  to  quite  as  good  advantage,  and  will  probably  not 
put  in  more  than  from  forty  to  fifty  cubic  yards  per  day.  It 
would  therefore  be  somewhat  more  economical  to  work  two 
gangs  of  eleven  men  each  on  separate  sets  of  platforms,  espe- 
cially as  in  this  way  a  rivalry  is  created.  Lack  of  room,  however, 
will  frequently  preclude  this  arrangement. 

322.  COST  OF  MIXING  BY  HAND.  —  The  amount  of  concrete 
stated  above,  two  and  a  half  yards  per  man,  may  be  taken  as 
a  maximum.  With  wages  at  $1.75  per  day  this  would  corre- 
spond to  a  cost  of  about  seventy  cents  per  yard,  exclusive  of 
the  wages  of  a  foreman.  Numerous  examples  might  be  cited 
where  the  mixing  costs  more.  Colonel  MendeLl,  in  writing  of 
the  fortifications  at  Fort  Point,  California,1  states  that  a  fore- 
man (at  $4  per  day)  and  twenty  laborers  (at  $2  per  day)  made 
forty-five  cubic  yards  per  day  of  eight  hours,  the  cost  of  mixing 
being  thus  about  $1  per  cubic  yard.  It  is  stated  that  "the" 
circumstances  were  exceptionally  favorable." 

As  an  instance  where  hand  mixing  was  done  at  a  very  low 
cost,  the  Lonesome  Valley  Viaduct 2  may  be  mentioned.  At 


1  Jour.  Assn.  of  Engr.  Soc.,  March,  1895. 

2  Construction  of  Substructure  for  Lonesome  Valley  Viaduct,  Gustave  R. 
Tuska,  Trans.  A.  S,  C.  E.,  Vol.  xxxiv,  p.  24?, 


MACHINES  FOR  MIXING  207 

this  point  colored  labor  was  used  at  a  cost  of  $1  for  eleven  hours' 
work.  A  gang  of  men,  distributed  as  follows,  would  mix  and 
lay  forty  cubic  yards  of  concrete  per  day:  — 

Filling  sand  barrows  and  handling  water 1 

Filling  rock  barrows 2 

Mixing  sand  and  cement 4 

Mixing  stone  and  mortar 4 

Wheeling  concrete 2 

Spreading  concrete  in  the  molds 1 

Tamping  concrete  in  the  molds 1 

Foremen 1 

Total 4(5 

Fifteen  men  at  $1  per  day,  and  foreman  at  $2.50  per  day, 
makes  a  cost  of  $17.50  for  forty  yards  of  concrete,  or  at  the 
rate  of  forty-four  cents  a  yard  for  mixing.  Had  the  laborers 
received  $1.75  per  day,  however,  the  cost  would  have  been  72 
cents  per  yard. 

323.  In  the  construction  of  the  Forbes  Hill  Reservoir  and 
stand  pipe  at  Quincy,  Mass.,1  all  concrete  was  mixed  and  placed 
by   hand.     "The   ordinary   concrete   gang   was   made   up   of   a 
sub-foreman,  two  men  gaging  materials,  two  men  mixing  mor- 
tar, three  men  turning  the  concrete,  three  men  wheeling  con- 
crete, one  man  placing,   and  two  men  ramming.     Two  gangs 
were  ordinarily  employed,   placing  about  twenty   cubic  yards 
per  day  each,  or  about  1.43  cubic  yards  per  man.     The  con- 
crete was  turned  at  least  three  times  before  placing."     With 
labor  at  $1.75  per  day,  this  would  give  the  cost  of  mixing  and 
placing  $1.22  per  cubic  yard.     The  actual  cost  of  mixing  and 
placing  varied  from  $0.97  to  $1.53,  according  to  the  character 
of  the  work. 

ART.  42.     CONCRETE  MIXING  MACHINES 

324.  General  Classification.  —  Concrete  mixing  machines  may 
be  divided  into  two  general  classes,  batch  mixers  and  continu- 
ous mixers.     In  the  former,  sufficient  materials  are  proportioned 
to  make  a  convenient  sized  batch  for  the  mixer.     They  are  then 
charged  into  the  machine  at  once,  given  a  certain  amount  of 
mixing,  and  then  discharged  at  once.     In  the  continuous  mixers 


1  Described  by  C.  M.  Saville,  M.  Am.  Soc.  C.  E.,  Engineering  News,  Mar. 
13,  1902. 


208  CEMENT  AND  CONCRETE 

the  materials  are  dumped  on  a  platform,  and  after  being  prop- 
erly proportioned,  are  delivered  gradually  to  the  mixer,  and  if 
fed  uniformly,  the  concrete  is  discharged  continuously  by  the 
machine.  In  the  latter  method  care  must  be  taken  to  feed 
the  cement,  sand  and  stone  together  and  at  a  uniform  rate. 
If  one  man  shovels  cement,  two  men  shovel  sand  and  four  men 
handle  the  stone,  and  the  cement  man  stops  to  fill  his  pipe, 
there  is  likely  to  be  a  poor  streak  of  concrete.  It  is  therefore 
desirable  in  feeding  a  continuous  mixer  to  spread  the  measured 
quantity  of  stone  on  the  platform,  and  on  top  of  this  place  the 
weighed  quantities  of  sand  and  cement.  Then  if  each  shoveler 
gets  his  shovel  blade  under  the  whole  mass,  he  will  have  some 
of  each  ingredient. 

325.  There  are  many  styles  of  concrete  mixers  of  both  classes 
on  the  market.     One  of  the  oldest,  as  well  as  one  of  the  best, 
is  the  cubical  box  mixer  which  consists  of  a  box  four  or  five 
feet  on  a  side,  supported  by  trunnions  at  opposite  corners,  and 
made  to  revolve  about  this  axis.     A  hinged  door  is  provided 
near  one  corner  of  the  box  by  which  the  latter  is  charged  and 
emptied.     The  dry  materials  ma}'  be  first  charged  and  mixed 
and  the  water  added  later,  either  through  the  door  or  through 
a  perforated  pipe  in  the  axis,  or  the  water  may  be  added  with 
the  dry  materials;  after  from  ten  to  thirty  revolutions  of  the 
box,  the  mixed  concrete  is  discharged  into  a  skip  or  on  a  car, 
to  be  conveyed  to  the  place  of  deposition. 

The  great  merit  of  this  mixer  is  that  the  materials  are  thrown 
back  and  forth  from  one  side  of  the  cube  to  another  and  a 
thorough  commingling  results.  The  chief  disadvantage  is  the 
difference  in  elevation  between  the  receiving  hopper  and  point 
of  delivery,  making  it  necessary  to  elevate  the  materials;  one 
other  defect  is  that  the  batch  is  not  in  view  while  being  mixed, 
so  that  the  amount  of  water  cannot  be  regulated  according  to 
slight  variations  that  may  occur  in  the  moisture  of  the  sand  and 
stone  when  charged. 

326.  To  obviate  this  latter  difficulty  as  well  as  to  facilitate 
to  some  extent  the  charging  and  dumping  of  the  batch,  a  form 
of  box  mixer  is  made  in  which  the  corners  of  the  box  in  the  axis 
of  revolution  are  truncated,  and  the  trunnions  are  replaced  by 
collars  which  support  the  box,  and  through  which  the  materials 
may  be  fed  and  discharged.      The  collars  are  supported  in  9 


MACHINES  FOR  MIXING  209 

tilting  cradle  which  permits  the  delivery  end  to  be  depressed 
after  the  batch  is  mixed.  The  advantage  of  having  the  batch 
visible  during  mixing  is  perhaps  somewhat  offset  by  the  greater 
difficulty  of  thoroughly  cleaning  the  box  when  discharged. 

Mixers  working  on  the  same,  principle  are  sometimes  made 
in  other  forms  than  the  cube.  One  of  these  is  the  cylindrical 
mixer,  which  is  made  of  boiler  plate  and  may  be  four  or  five  feet 
in  diameter  and  five  or  six  feet  long.  This  is  rotated  about  a 
diagonal  axis.  It  is  said  to  be  more  easily  and  cheaply  made 
than  the  cubical  mixer,  and  dumps  more  quickly  and  cleanly, 
while  the  cost  of  operation  is  about  the  same,  and  the  mixing 
is  as  satisfactorily  done  as  in  the  cubical  form. 

327.  The  so-called  "  Dromedary  Mixer  "  l   is  a  batch  mixer 
specially  designed  for  use  on  street  work.     The  mixing  chamber 
is  a  cylindrical  steel  drum  with  closed  ends,  mounted  between 
two  wheels.     It  is  hinged  along  an  element  of  the  cylinder  so 
that  it  opens  into  two  halves  like  a  clam  shell  bucket,  to  dis- 
charge.    A  trap  door  is  provided  for  filling.     The  cart  is  drawn 
by  a  horse,  and  the  chamber  may  be  thrown  in  or  out  of  gear 
with  the  cart  wheels.     The  cement  and  sand  being  first  added 
and  the  trap  door  closed,  the  horse  draws  the  cart  to  the  stone 
pile.     The  stone  and  water  are  here  added  and  the  cart  is  drawn 
to  the  work;  the  concrete,  mixed  on  the  way,  is  dumped  by  the 
driver,  who  merely  raises  a  lever  which  not  only  separates  the 
two  halves  of  the  mixer,  but  throws  it  out  of  gear  so  that  it 
stops  revolving.     The  chamber  may  be  thrown  out  of  gear  at 
any  time  without  dumping  if  desired. 

328.  The  Ransome  Concrete  Mixer2  " consists  of  a  hollow 
rotary  dome,  having  upon  the  inner  surface  of  its  periphery 
directing  guides  or  flanges,   and  hinged  shelves,  by  means  of 
which  the  materials  are  thrown  together  and   perfectly  com- 
mingled.    A  discharge  chute,  or  spout,  is  arranged  to  deliver  the 
material  into  the  barrow  or  cart  when  properly  mixed."     The 
mixer  is  also  provided  with  an  automatic  device  for  proportion- 
ing the  materials,  and  a  conveyor  to  carry  them  to  the  mixer. 
Water  is  supplied  to  the  mixer  through  a  pipe  with  facilities 
for  regulating  the  supply. 


1  Fisher  and  Saxton,  123  G  St.,  N.  E.,  Washington,  D.  C. 

2  Ransome  Concrete  Machinery  Co.,  11  Broadway,  N.  Y. 


210  CEMENT  AND  CONCRETE 

329.  The  Smith  Mixer l  is  a  batch  machine   made  of  two 
truncated  cones  placed  base  to  base,  and  provided  on  the  in- 
terior with  deflecting  plates  designed  to  throw  the  materials 
from  one  end  of  the  mixer  to  the  other  as  the  machine  is  re- 
volved.    At  the  junction  of  the  two  cones,  on  the  outer  cir- 
cumference, is  a  spur  gear  by  which  the  chamber  is  actuated. 
The  latter  rests  upon  rollers  in  a  swinging  frame,  so  arranged 
that  the  machine  may  be  tilted  for  dumping  while  the  drum  is 
revolving.     In  operating  this  mixer  it  has  been  found  advanta- 
geous to  charge  the  broken  stone  or  gravel  first,  and  give  one  or 
two  revolutions  before  adding  the  cement  and  sand,  as  this  cleans 
the  mortar  from  the  corners.     This  form  seems  to  be  particularly 
adapted  for  a  portable  machine.     They  may  be  had  mounted 
on  trucks,  with  or  without  an  engine,  as  desired. 

330.  The  McKelvey  Mixers2  are  made  in  two  styles,  con- 
tinuous  and   batch.     Both   styles   are   cylinders   revolving   on 
friction  rollers,  and  having,  on  the  interior,  deflecting  blades 
and  a  patent  " gravity  shovel"   which  lies  against  the  rising 
side  of  the  drum  and  casts  the  materials  downward  when  the 
cylinder  has  revolved  far  enough  to  overturn  the  blade.     The 
batch  mixer  has  a  shorter  cylinder  and  can  be  discharged  at 
will.     These  mixers  may   be   fed   by  shovels,  or  they   may  be 
provided  with  a  hopper  into  which  the  materials  may  be  dumped 
from    carts    or   barrows.     They   discharge  directly  into   wheel- 
barrows.    The  mixer,  and  an  engine  and  boiler  to  run  it,  are 
mounted  compactly  on  a  truck,  or  the  mixer  is  furnished  on  a 
steel  frame  without  an  engine. 

331.  The  pan  mixer3  consists  of  a  large  shallow  pan  into 
which  may  be  lowered  a  framework  carrying  a  series  of  plows. 
The  materials  are  spread  in  the  pan  in  layers,  the  plows  are 
lowered  into  it,  and  the  pan  is  revolved  about  its  vertical  axis, 
the  plows  remaining  stationary.     The  plows  are  so  arranged  as 
to  move  the  materials  radially  toward  and  away  from  the  cen- 
ter of  the  pan.     The  water  may  be  added  from  a  rose  nozzle. 
For  dumping,  an  opening  is  made  in  the  bottom  of  the  pan  by 
withdrawing  a  slide.     Were  the  plows  made  to  revolve  in  a 


1  Contractors'  Supply  Co.,  232  Fifth  Ave.,  Chicago. 

2  McKelvey  Concrete  Machinery  Co.,  N.  Y.  Life  Bldg.,  Chicago. 


Clyde  Iron  Works,  Duluth,  Minn. 


MACHINES  FOR  MIXING  211 

stationary  pan,  the  concrete  would  be  more  conveniently 
dumped  in  a  pile,  or  in  a  car,  instead  of  being  scattered  about 
under  the  pan. 

332.  The  Cockburn,1  a  continuous  mixer,  is  in  the  form  of  a 
long  box  square  in  cross-section,  surrounded  at  either  end  by 
circular  rings  supported  on  friction  rollers.     By  suitable  gear- 
ing the  mixer  is  revolved  about  its  longest  axis,  which  has  a 
slight  inclination  toward  the  discharge  end.     The  materials  are 
added  through  a  hopper  at  one  end,  and  fall  from  one  side  of 
the  box  to  the  adjacent  side  as  the  machine  revolves,  working 
gradually  toward  the  delivery  end,  which  is  open.     The  water 
is  added  through  a  pipe  at  about  one-third  of  the  length  of  the 
box  from  the  feed  end.     While  this  machine  has  no  complicated 
system  of  blades  to  become  clogged,  the  mortar  has  a  tendency 
to  stick  in  the  corners  of  the  mixer,  making  the  interior  cylin- 
drical,  and  thus  much  less  effective  in  mixing.     Striking  the 
sides  of  the  box  with  a  heavy  hammer  will  detach  the  mortar, 
and  this  requires  occasional  attention. 

333.  A  common  form  of  continuous  mixer  consists  of  a  screw 
working  in  a  cylinder.     The  materials  are  fed  to  the  cylinder 
near  one  end  and  are  mixed  while  being  gradually  worked  toward 
the  other  end  by  the  screw.     The  water  is  added  through  a 
fixed  perforated  pipe  at  a  point  about  one-third  of  the  distance 
from  the  feed  end  of  the  cylinder,  and  the  mixed  concrete  falls 
from   the   outlet   at   the   other   end.     This   style   is   frequently 
made  in  a  light  form  and  mounted  on  wheels,  and  is  then  con- 
venient in  the  laying  of  concrete  for  pavements. 

A  modification  of  the  screw  mixer  consists  of  a  semi-cylin- 
drical trough,  in  which  revolves  a  shaft  carrying  blades  set  at 
right  angles  to  the  shaft  and  to  each  other.  The  trough  is 
sometimes  given  a  slight  inclination  to  the  horizontal,  and  the 
blades  are  so  shaped  as  to  assist  in  working  the  materials  toward 
the  delivery  end. 

334.  The  Drake  Mixer2  is  of  the  general  form  just  described. 
One  of  the  machines  made  by  this  company  is  a  semi-cylindrical 
trough  in  which  revolve  in  opposite  directions  two  shafts,  each 
carrying  some  thirty  blades.     Most  of  the  blades  are  straight, 


1  Cockburn  Barrow  and  Machine  Co.,  Jersey  City,  N.  J. 

2  Drake  Standard  Machine  Works,  298-302  W.  Jackson  Boul.,  Chicago. 


212  CEMENT  AND  CONCRETE 

but  some  of  them  are  curved  to  work  the  material  toward  the 
delivery  end. 

335.  Gravity  Mixer.  —  An  appliance  recently  devised,  which 
is  called  a  concrete  mixer,  consists  of  a  steel  trough  provided 
with  staggered  pins  and  deflecting  plates.     The  trough  is  sup- 
ported in  an  inclined  position  and  has  a  hopper  at  its  upper 
end.     Water  is  supplied  through  spray  pipes  at  the  side  of  the 
trough.     The  materials,  stone,  sand  and  cement,  are  spread  in 
layers  on  the  mixing  platform,  with  the  stone  at  the  bottom. 
The  materials  are  then  thrown  into  the  hopper;  they  are  mixed 
as  they  descend  through  the  pins,  and  the  product  is  caught  in 
barrows  or  carts  at  the  bottom. 

336.  In  a  very  able  article  on  concrete  mixers,1  Mr.  Clarence 
Coleman,  M.  Am.  Soc.  C.  E.,  makes  an  analytical  discussion  of 
the  relative  efficiencies  of  the  several  forms.     In  this  analysis 
he  gives  the  following  weights  to  the  several  requirements  for 
a  perfect  mixer.     That  the  entire  mass  of  concrete  shall  be  so 
commingled   that   the   cement   shall   be   uniformly   distributed 
throughout  the  batch. is  given  a  weight  of  forty;  that  the  amount 
of  water  shall  be  subject  to  control  is  given  a  weight  of  twenty- 
five;  perfect  dry  mixing  and  relative  time  of  mixing,  each  ten; 
and  receiving  materials,  discharging  concrete  and  self-cleaning, 
are  each  given  a  weight  of  five. 

The  first  three  requirements,  with  a  combined  weight  of 
seventy-five,  relate  to  the  production  of  good  concrete,  while 
the  remaining  requirements,  with  a  combined  weight  of  twenty- 
five,  pertain  to  economy  in  use.  In  short,  the  first  requisite 
is  that  a  machine  shall  be  capable  of  producing  a  perfect  mix- 
ture; then  the  machine  that  accomplishes  this  result  at  the 
lowest  cost  per  cubic  yard  is  the  best.  The  choice  of  a  machine 
will  depend  frequently  on  the  character  of  the  work  to  be  done, 
as  some  machines  can  only  be  used  economically  where  large 
quantities  of  concrete  are  to  be  used  in  a  restricted  area,  while 
others  are  particularly  adapted  for  portable  plants. 

ART.  43.     CONCRETE  MIXING  PLANTS  AND  COST  OF  MACHINE 

MIXING 

337.  Coosa  River  Improvement.  —  The  concrete  plant  used 
at  Lock  No.  31,  Coosa  River  Improvement,2  was  erected  in  a 


1  Engineering  News,  Aug.  27,  1903. 

2  Major  F.  A.  Mahan,  Corps  of  Engineers,  U.  S.  A.,  in  charge. 


CONCRETE  PLANTS  213 

three-story  shed.  The  top  story  served  as  a  cement  storage 
room  and  two  hoppers  were  arranged  in  the  floor  to  receive 
the  cement  for  the  mixers  below.  Level  with  the  floor  of  the 
second  story  were  two  other  hoppers  immediately  below  the 
cement  hoppers,  to  receive  the  sand  and  broken  stone,  while  in 
the  first  story  or  basement  the  mixers  were  suspended  at  a 
height  sufficient  to  allow  concrete  cars  to  pass  under  them. 
The  following  description  is  from  the  report  of  the  designer, 
Mr.  Charles  Firth,  U.  S.  Asst.  Engineer: 1 

"The  cars  used  in  handling  the  sand  and  broken  stone  are 
of  the  side  dump  pattern  and  are  brought  into  the  charging 
room  on  either  side  of  the  hoppers.  The  cement  is  drawn  from 
the  cement  room  overhead  In  proper  quantities,  through  verti- 
cal chutes  arranged  somewhat  on  the  principle  of  the  old- 
fashioned  powder  flask. 

"The  water  is  added  to  the  materials  as  they  enter  the  mix- 
ers, and  the  quantity,  which  will  probably  be  variable  with 
the  temperature,  is  controlled  by  valves  on  the  mixing  floor, 
the  operators  being  governed  by  indicators,  which  show  the 
quantity  used.  The  mixers  are  cubical  boxes  four  feet  on  each 
side,  inside  measurement,  made  of  steel  plate  five-sixteenths  of 
an  inch  thick,  with  2£  by  2J-inch  angle  irons.  Each  mixer  is 
provided  with  a  door  in  one  corner,  twenty-two  inches  square, 
fastened  with  a  tempered  steel  spring  catch,  and  held  open 
when  required  with  a  hinged  screw  bolt.  The  shaft  which 
revolves  the  mixers  is  three  inches  square.  It  is  securely 
fastened  to  them  by  trunnion  castings  at  diagonally  opposite 
corners.  The  whole  is  driven  by  a  10  by  16  inch  horizontal 
engine,  and  thrown  in  and  out  of  gear  by  ordinary  friction 
gearing  with  friction  and  brake  levers. 

"After  a  sufficient  number  of  revolutions  in  the  mixers,  the 
concrete  is  dumped  into  the  concrete  cars  below,  which  are  of 
the  center  dump  pattern." 

The  method  given  of  measuring  the  cement  is  not  recom- 
mended, as  the  charge  of  cement,  if  not  a  full  barrel,  should 
always  be  weighed.  The  three-story  arrangement  by  which 
the  materials  were  handled  almost  entirely  by  gravity  was 
made  possible  by  the  high  bank  at  the  side  of  the  lock  pit. 


1  Annual  Report,  Chief  of  Engineers,  U.S.A.,  1894,  p.  1292. 


214  CEMENT  AND  CONCRETE 

The  total  cost  of  the  plant,  exclusive  of  the  boilers,  is  stated 
to  have  been  about  $8,000,  and  the  average  output  about  two 
hundred  cubic  yards  of  concrete  per  day  of  eight. hours.  The 
cost  of  mixing,  depositing  and  ramming  8,710  cubic  yards  of 
concrete  in  the  construction  of  lock  walls  was  at  the  rate  of 
$0.884  per  cubic  yard. 

338.  Portland,  Maine,  Defenses.  —  In  the  construction  of  the 
defenses   at   Portland,    Maine,1   a   five-foot   cubical   mixer   was 
used.     Sand  and  stone  were  delivered,   by  bucket  conveyors, 
in  bins   directly   over   the   mixer.     "  Immediately   under  these 
bins  were  two  measuring  hoppers  for  stone  and  sand,  respec- 
tively, and  an  additional  hopper  for  cement.     From  these  meas- 
uring  hoppers   the    charge   was   dumped   into   the    mixer   and 
thence,  when  mixed,  into  a  car  immediately  under  it.     This  car 
delivered  the  mixed  batch  by  means  of  a  hoisting  engine  and 
an  inclined  track  to  the  site  of   the  battery  under  a  fifty-five 
foot  derrick,  which  placed  it  in  the  work  at  the  point  required. 
Two  barrels  of  cement,  sixteen  cubic  feet  of  sand,  and  thirty- 
two  cubic  feet  of  stone  constituted  a  batch.  *  *-*     The  usual 
number  of  men  engaged  in  the  operation  of  mixing  and  placing 
was  as  follows:  — Two  master  laborers,  three  steam  engineers, 
two   stokers   and   twenty-five   laborers."     It    is  said  that   200 
barrels  of  cement,  or  100  batches,  could  be  mixed  and  placed  in 
a  day  of  eight  hours.     This  would  make  the  labor  cost  of  this 
portion  of  the  work  50  or  60  cents  per   cubic  yard.     The  cost 
stated,  however,  varies  greatly  according  to  the  amount  of  detail 
in  construction,  and  the  lowest  cost  given  for  "  labor  of  mixing 
and  placing"  is  $1.15  per  cubic  yard. 

339.  San  Francisco  Defenses.  —  A  cubical  mixer  used  in  the 
construction  of  the  defenses  at  San  Francisco 2  mixed  250  cubic 
yards  per  day  with  seven  men,  engineer,  fireman,  and  five  men 
to  feed  and  dump  mixer,  at  a  labor  cost  of  $14.67  per  day,  or 
about  six  cents  per  cubic  yard,  exclusive  of  cost  of  transporta- 
tion and  ramming.     The  materials  and  concrete  were  handled 
on  cars  run  almost  entirely  by  gravity. 

340.  Buffalo  Breakwater.  —  In  the  construction  of  the  Buf- 


1  Report  of  Charles  P.  Williams  to  Maj.  Solomon  W.  Roessler,  Corps  of 
Engrs.,  U.  S.  A.,  in  charge.     Report  Chief  of  Engineers,  1900,  p.  745. 

2  Maj.  Charles  E.  L.  B.  Davis,  Corps  of  Engineers,  U.  S.  A.,  Report  Chief  of 
Engrs.,  1900,  p.  980. 


CONCRETE  PLANTS 


215 


falo  Breakwater/  the  mixing  plant,  consisting  of  a  cubical 
mixer  with  necessary  engines  and  boilers  and  two  derricks, was 
mounted  on  a  dismantled  lake  schooner  which  could  be  placed 
beside  the  section  of  the  breakwater  under  construction.  The 
broken  stone  was  delivered  in  a  canal  boat  which  could  be  tied 
up  alongside  the  schooner,  and  outside  of  the  canal  boat  lay  the 
material  scow.  The  latter  was  made  from  an  old  dump  scow, 
the  decked  pockets  serving  as  bins  for  cement,  sand  and  gravel. 
Into  a  steel  bucket  on  the  scow  were  loaded,  by  wheelbarrows, 
the  following  materials: 

5.4  cu.  ft.  (H  bbls.)  cement. 
10.8  cu.  ft.  sand. 

5.4  cu.  ft.  gravel. 
21.0  cu.  ft.  total. 

Into  a  similar  bucket  on  the  canal  boat  21.6  cubic  feet  of 
broken  stone  were  shoveled.  As  these  buckets  were  filled,  they 
were  hoisted  by  one  of  the  derricks  and  dumped  into  the  cubical 
mixer.  The  latter  discharged  the  mixed  concrete  into  a  skip 
and  a  derrick  deposited  the  concrete  in  place.  The  cost  of  labor 
per  cubic  yard  of  concrete  is  as  follows: 


ITEMS. 

No. 
MEN. 

COST 

PER 

Horn. 

Cu.  YDS. 

PKB 

HOUR. 

COST  o* 
LABOK 

PER 

Cu.  YD. 

Loading  material  into  buckets  from  scows 
Mixing,  including  engine  men  and  derrick 
men  .         

18 
11 

$S.17J 
2.85 

18.2 
182 

.$0.174 
0  l'?Q 

Placing,  includinop  foreman     .         ... 

13 

2.05 

182 

0  146 

Total  labor 

42 

88  17£ 

182 

•*0  449 

The  above  does  not  include  cost  of  fuel,  nor  of  transporting 
materials  from  the  storehouses  or  yards  to  the  site  of  the  work. 

341.  Quebec  Bridge.  —  The  plant  used  in  the  construction 
of  the  Quebec  Cantilever  Bridge3  consists  of  a  No.  5  rotary 
stone  crusher,  with  a  maximum  capacity  of  thirty  cubic  yards 
per  hour,  discharging  into  a  bucket  conveyor  which  delivered 
the  crushed  stone  in  a  small  storage  bin  directly  over  the  con- 
crete mixer.  The  latter  was  of  the  cubical  form,  five  feet  on  a 
side,  with  a  capacity  of  two  cubic  yards  of  concrete  per  batch. 


1  Emile  Low,  U.  S.  Asst.  Engr.,  Engineering  News,  Oct.  8,  1903. 
1  Engineering  News,  Jan.  29,  1903. 


216  CEMENT  AND  CONCRETE 

The  cement  warehouse  and  the  sand  supply  were  near  the 
mixer.  Cement  and  sand  were  hoisted  to  the  top  of  the  ma- 
chine in  boxes,  with  bottoms  inclined  at  forty-five  degrees, 
each  holding  a  batch,  and  dumped  into  the  charging  hopper  of 
the  mixer  as  required.  The  mixer  was  elevated  sufficiently  to 
permit  dumping  the  concrete  directly  in  a  skip  on  a  car,  the 
latter  being  run  to  the  work.  The  skip  was  handled  by  guy 
derricks.  This  plant  made  the  remarkable  record  of  two  hun- 
dred eighty-five  batches  in  ten  hours,  and  on  one  occasion 
turned  out  one  hundred  fifty  batches  in  five  hours,  or,  if  all 
were  two-yard  batches,  at  the  rate  of  sixty  yards  per  hour. 

342.  Galveston.  —  For  the  construction  of  the  Galveston  sea 
wall  two  concrete  mixing  and  handling  machines  were  designed,1 
each  consisting  of  a  double-deck  car,  on  eight  wheels,  with  two 
revolving  derricks,   one  on  either  side  for  handling  materials 
and    concrete,    respectively.     The    materials    are    delivered    on 
tracks  beside  the  mixer  car  track  which  is  parallel  to  the  sea 
wall.     One  derrick  hoists  the  loaded  skips  from  the  material 
cars  and  deposits  them  on  the  upper  deck  of  the  mixer  car, 
whence  they  are  delivered  in  measured  quantities  to  the  Smith 
Rotary  Mixer  located  on  the  lower  deck.     When  mixed,   the 
concrete  is  dumped  into  a  skip,  which  is  handled  by  the  second 
derrick  and  dumped  into  the  forms. 

343.  For   work   having   similar   requirements    to    that    just 
described,  namely,  for  retaining  walls  on  track  elevation,  Chicago 
&  Western  Indiana  R.  R.  at  Chicago,  the  problem  was  met  in 
a  somewhat  different  manner.2     An  ordinary  flat  car  was  double 
decked  and  the  space  between    decks  inclosed  to  protect  the 
machinery,  including  the  Drake  Concrete  Mixer.     Cars  contain- 
ing cement,  sand  and  stone  were  coupled  in  the  rear  of  the  mixer 
car.     These  material  cars  were  fitted  with  removable  wheeling 
platforms,  making  a  complete  runway  along  the  sides  of  the 
cars.     The  materials  were  delivered  at  the  mixer  car  in  wheel- 
barrows and  dumped  into  measuring  boxes,  and  thence  fed  to 
the   mixer.     The   concrete  was   delivered  on   a  belt   conveyor 
mounted  on  a  boom  with  turntable  permitting  nearly  half  of  a 
revolution.     The  outer  end  of  the  conveyor  could  be  raised  or 
lowered  as  desired,  and  the  concrete  was  thus  deposited  where 


1  Engineering  News,  Jan.  15,  1903. 
3  Ibid.,  Feb.  28,  1901. 


COST  OF  CONCRETE 


217 


needed  in  the  work.  To  permit  the  mixer  train  to  move  along 
the  track,  the  two  ends  of  a  cable  were  made  fast  to  anchorages 
placed  about  a  thousand  feet  apart,  one  in  front  of,  and  the 
other  behind,  the  train.  As  this  cable  had  about  eight  turns 
around  a  winding  drum  on  the  mixer  car,  the  train  could  be 
propelled  forward  or  backward  at  will. 

A  somewhat  similar  form  has  been  used  for  street  work, 
where  the  mixer  and  electric  motor  are  mounted  on  a  truck 
with  a  swinging  conveyor  for  the  delivery  of  concrete  anywhere 
between  the  curbs.  A  pair  of  wheels  in  the  rear  serve  to  carry 
an  inclined  runway  for  wheelbarrows  by  which  the  materials 
are  delivered  to  the  mixer. 

344.  The  data  for  the  following  items  concerning  the  cost  of 
mixing  concrete  for  culverts  on  railroad  work  are  taken  from 
an  article  in  Engineering  News.1 

"The  plant  is  located  on  a  hillside  with  the  crusher  bins 
above  the  loading  floor  or  platform  that  extends  over  the  top 
of  the  mixer,  so  that  crushed  stone  can  be  drawn  directly  from 
the  chutes  of  the  bins  and  wheeled  to  the  mixer.  The  sand  is 
hauled  up  an  incline  in  one-horse  carts  and  dumped  on  the? 
floor,  and  is  also  wheeled  in  barrows  to  the  mixer."  The  capa- 
city of  the  cubical  mixer  used  was  seven-eighths  cubic  yard.  The 
cost  of  mixing  and  placing  was  as  follows: 


ITEMS. 

COST 

PER 

DAY. 

COST 

PKIl 

Cu.Yi>. 

One  foreman  assumed  at  82  50  per  day 

$2.50 

Three  men  supplying  mixer  at  SI  50  per  day 

4.50 

One  engineman  assumed  at  S2  00  per  day 

2.00 

Fuel  and  supplies  assumed  at                   .                 .... 

2.00 

Cost  of  mixing  40  cu.  yds.                                 

SI  1.00 

SO  275 

Two  men  loading  wheelbarrows  at  SI  50      

$3.00 

Four  men  wheeling  wheelbarrows  at  8.1.  50         

6.00 

Cost  of  wheeling  40  cu.  yds.  100  feet    

$9.00 

0225 

Four  men  ramming  at  $1.50     
Four  men  wheeling  in  and  bedding  large  stone  in  concrete  at 
$1.50     .      . 

86.00 
600 

0.150 
0  150 

Total  cost  mixing  and  placing 

80  800 

1  Location  and  Construction  of  the  Ohio  Residency,  Pittsburg,  Carnegie 
&  Western  R.R.,  Engineering  News,  May  21,  1903. 


218  CEMENT  AND  CONCRETE 

It  is  not  explained  why  six  men  are  required  to  load  and 
wheel  forty  cubic  yards  one  hundred  feet  in  ten  hours,  but  it 
may  be  that  these  men  assisted  in  other  operations. 

Another  contractor  on  the  same  work  used  a  different  form 
of  mixer  with  much  lower  loading  platform  and  handled  the 
mixed  concrete  with  skips  and  derrick.  The  cost  is  estimated 
as  follows: 

1  man  feeding  mixer $1.50 

1  engineman  assumed  at      2.50 

1  derrick  man  assumed  at    . 2.50 

2  tagmen  swinging  boom  and  dumping 3.00 

6  barrowmen  supplying  mixer 9.00 

2  men  tamping 3.00 

Fuel,  supplies,  etc.        1.50 

Cost  of  mixing  and  placing  50  cu.  yds.      .    .    $23.00 
Cost  per  cu.  yd.,  46  cents. 

ART.  44.     COST  OF  CONCRETE 
345.  QUANTITIES  OF  INGREDIENTS  IN  A  CUBIC  YARD.  — As 

has  already  been  indicated,  the  rational  method  of  proportion- 
ing concrete  is  to  use  just  sufficient  mortar  to  fill  the  voids  in 
the  stone,  or  possibly  a  very  small  excess  to  allow  for  imperfect 
mixing;  and  in  ordinary  practice  this  rule  should  not  be  de- 
parted from  unless  it  be  for  some  special  reason.  When  so  pro- 
portioned, a  cubic  yard  of  concrete  will  contain  approximately 
a  cubic  yard  of  stone,  depending  on  the  method  of  measure- 
ment. If  we  know  the  percentage  of  voids  in  the  broken  stone 
or  gravel,  and  consequently  the  percentage  of  mortar  which 
should  be  found  in  a  cubic  yard  of  the  finished  concrete,  we 
may  readily  obtain  the  approximate  cost  per  cubic  yard  of  the 
latter  for  a  given  quality  of  mortar  and  given  unit  prices. 

Thus,  suppose  we  have  stone  in  which  the  voids  are  such 
that  the  mortar  will  amount  to  forty  per  cent,  of  the  finished 
concrete,  and  we  wish  to  have  the  mortar  composed  of  three 
volumes  of  loose  sand  to  one  volume  packed  natural  cement, 
unit  prices  being  as  follows: 

Cement,  $1.25  per  barrel  of  300  pounds  net,  3.75  cubic  feet. 

Sand,  $1.00  per  cubic  yard. 

Stone,  $1.75  per  cubic  yard. 

As  in  §  290,  we  find  the  ingredients  in  one  cubic  yard  of 


COST  OF  CONCRETE  219 

mortar  to  cost  $3.33.  Since  forty  per  cent,  of  the  concrete  is 
to  be  composed  of  mortar,  the  mortar  in  one  cubic  yard  of 
concrete  will  cost  forty  per  cent,  of  $3.33,  or  $1.33,  and  one 
yard  of  stone  at  $1.75  will  make  the  total  cost  of  the  materials 
in  the  concrete  $3.08  per  cubic  yard. 

The  diagram  herewith  may  be  used  to  get  the  approximate 
cost  of  the  concrete  after  having  obtained  the  cost  of  the  mortar 
as  before.  Thus,  if  we  enter  the  diagram  with  the  cost  of  mor- 
tar $3.33,  and  follow  it  to  the  diagonal  line  marked  forty  per 
cent.,  we  find  this  is  on  the  ordinate  $2.33,  the  cost  of  the  in- 
gredients in  one  cubic  yard  of  concrete  when  the  stone  costs 
one  dollar  per  cubic  yard.  Hence,  $2.33  plus  $0.75  equals 
$3.08,  the  approximate  cost  of  the  materials  in  a  cubic  yard  of 
the  concrete  as  desired. 

346.  The  usual  method,  however,  of  stating  proportions  in 
concrete  is  to  give  the  volumes  of  sand  and  stone  to  one  volume 
of  cement.  Thus,  one  of  cement,  three  of  sand  and  six  of  stone 
would  usually  mean  one  volume  of  packed  cement,  three  vol- 
umes of  loose  sand  and  six  volumes  of  loose  broken  stone.  To 
arrive  at  the  cost  of  concrete  when  proportions  are  thus  ar- 
bitrarily stated,  involves  a  greater  amount  of  work.  From  the 
tables  already  given  (Art.  36),  we  can  determine  the  amount  of 
mortar  which  a  given  quantity  of  dry  ingredients  will  make, 
and  the  consequent  cost  of  the  mortar  per  cubic  yard.  Then  a 
knowledge  of  the  voids  in  the  broken  stone  will  permit  of  a 
close  estimate  of  the  amount  of  concrete  made,  whence  we  can 
determine  the  cost  of  the  latter. 

For  example,  suppose  it  is  desired  to  determine  the  cost  of 
the  materials  in  a  cubic  yard  of  natural  cement  concrete  under 
the  following  conditions: 

1  bbl.  cement  containing  280  pounds  net,  at  $1.00  per  bbl. 

3  bbls.  sand  weighing  100  pounds  per  cu.  ft.,  at  $.75  per  cu.  yd. 

6  bbls.  loose  broken  stone,  having  45  per  cent,  voids,  at  $1.25  per  cu.  yd. 

1  bbl.    cement  =    3.75  cu.  ft.  =  .139  cu.  yd.,  cost  $1.000 

3  bbls.  sand      =  11.25  cu.  ft.  =  .417  cu.  yd.,  cost      .313 

6  bbls.  stone      =  22.50  cu.  ft.  =  .833  cu.  yd.,  cost    1.041 

Total  cost $2.354 

From  Table  61,  §  286,  we  find  that  it  requires  2.03  barrels  of 
cement  to  make  one  cubic  yard  of  one-to-three  mortar,  when 


220 


CEMENT  AND  CONCRETE 


CONCRETE   MAKING 
Cost  of  Concrete,   Dollars   per   Cu.  Yd. 
Stone   Assumed  to   Cost   $1.00  per   Cu.   Yd. 


EXAMPLES  OF  COST  221 

proportions  are  stated  as  above;  then  one  barrel  of  cement 
would  make  -  -  =  .493  cu.  yd.  As  forty-five  per  cent,  of  the 

Z.Oo 
stone  is  voids,  the  amount  of  solid  stone  in  six  barrels  would 

be  — or"     x  -55  =  .458  cu.  yd.     Then  the  mortar  plus  solid 

stone  would  be  .493  +  .458  =  .951  cu.  yd.  It  has  been  found 
by  experiment  that  the  amount  of  concrete  will  exceed  the  sum 
of  the  mortar  and  solid  stone  by  from  two  to  five  per  cent.; 
hence  we  may  assume  in  this  case  that  the  amount  of  concrete 
made  with  the  above  materials  would  be  .95  -f-  .03  =  .98  cu. 
yd.,  and  2.354  -*-  .98  =  $2.40,  the  cost  of  materials  in  one  cubic 
yard  of  finished  concrete.  To  obtain  the  actual  cost  of  con- 
crete in  place,  the  cost  of  mixing  and  deposition  must  be  added 
(see  Arts.  41  and  43).  When  the  volume  of  mortar  used  is  not 
greater  than  the  voids  in  the  loose  stone,  then  the  amount  of 
rammed  concrete  made  may  be  less  than  the  volume  of  loose 
broken  stone. 

347.  EXAMPLES  OF  ACTUAL  COST  OF  CONCRETE.  —  The  fol- 
lowing data  are  given  concerning  the  cost  of  concrete  on  several 
works  where  sufficient  details  have  been  published  to  be  of 
value. 

Defenses  Staten  Island.1  Cubical  box  mixer ;  proportions  by  vol- 
ume, 1  cement,  3  sand,  5  broken  stone;  5,609  cu.  yds.  of  concrete. 


ITEMS. 

COST  PER  Cu.  YD. 
CONCRETE  IN 
PLACE. 

Cement,  Portland,  at  $1.98  per  bbl.  . 

$2.546 

Broken  trap  rock     .            .            

1  041 

Sand  drawn  from  beach     .            

0.225 

Receiving  and  storing  materials  

0.149 

Mixing,  placing  and  ramming      

0.879 

Forms,  lumber  and  labor  .            

0.477 

Superintendence  and  miscellaneous         .... 

0.190 

Total  cost  per  cu.  yd  

.$5.507 

It  is  stated  that  hand  mixing  for  a  portion  of  the  concrete 
used  in  another  emplacement  cost  fifty-six  cents  more  per 
cubic  yard  than  machine  mixing. 


1  Major  M.  B.  Adams  in  charge.      Report  Chief  of  Engineers,   U.S.A., 
1900,  p.  837. 


222  CEMENT  AND  CONCRETE 

348.  Defenses  Tampa  Bay,  Florida.1  —  Cockburn-Barrow 
mixer,  with  cableway  for  placing  concrete.  Shell  concrete 
made  up  of  1  cement,  3^  sand  and  5^  shell. 

1.31  bbls.  cement,  at  $2.42  per  bbl $3.17 

.71  cu.  yd.  sand,  at  21  cents  per  cu.  yd .15 

1.08  cu.  yd.  shell,  at  50  cents  per  cu.  yd 5.4 

—     $3.86 
Labor  mixing $0.28 

Labor  placing  and  tamping .33 

Labor  on  forms    .  .155          .765 


Total  cost  per  cubic  yard $4.625 

The  above  does  not  appear  to  include  costs  of  running  ma- 
chinery, fuel,  repairs,  and  depreciation  of  plant. 

At  the  same  battery  2  in  the  following  year  the  cost  of  broken 
stone  and  shell  concrete  was  as  follows: 

.9    bbl.  cemsnt  at  $2.46  (including  $0.59  per  bbl. 

storage) $2.214 

.28  cu.  yd.  shell,  at  $0.45  per  cu.  yd .128 

.47       "       sand,  at    0.12      "         "         056 

.80       ."       stone,  at    2.95      "         "         2.360 

Total  materials $4.758 

Mixing  and  placing $0.623 

Forms 370 

Total .993 

Total  cost  per  cubic  yard $5.751 

349.  Defenses  San  Francisco,  Cal.3 — Cubical  mixer;  ma- 
terials drawn  from  bins  into  measuring  cars,  hoisted  by  elevator 
and  dumped  into  hopper  of  mixer.  Mixer  given  twelve  to  four- 
teen turns  and  concrete  dumped  into  cars,  pushed  by  hand  out 
on  trestles,  and  dumped  in  place.  Average  capacity  plant,  280 
cubic  yards  per  day  of  eight  hours.  Itemized  cost  of  8,328 
cubic  yards  of  concrete  in  place  was  as  follows: 


1  Report  Lieut.  Robert  P.  Johnson,  Corps  of  Engineers,  U.  S.  A.,  Report 
Chief  of  Engineers,  1899,  p.  906. 

2  Report  Lieut.  Frank   C.  Boggs,  Corps  of  Engineers,  U.  S.  A.,  Report 
Chief  of  Engineers,  1900,  p.  931. 

3  Maj.  Charles  E.  L.  B.  Davis,  Corps  of  Engineers,  in  charge.      Report 
Chief  of  Engineers,  1900,  p.  980f      ' 


EXAMPLES  OF  COST 


223 


.758  bbl.  Portland  cement,  at  $3.03  per  bbl    .    .    .      $2.298 

.887  cu.  yd.  rock,  at  $1.80  per  cu.  yd 1.597 

.41  cu.  yd.  sand,  at  0.73  per  cu.  yd .299 

Water .010 

Cost  of  materials $4.210 

Concrete  plant,  erection  per  cu.  yd.  concrete  .  .  $0.269 
Concrete  plant,  running  expenses  per  cu.  yd.  .  .  .022 
Concrete  plant,  taking  down .020 

Cost  for  plant,  exclusive  of  purchase 

price .311 

Forms  —  materials $0.272 

Forms  —  labor  in  erecting .346 

Forms  —  labor  taking  down .079 

Cost  forms .697 

Labor  mixing,  placing  and  ramming .626 

Total  cost  per  cubic  yard $5.844 

350.  In  the  building  of  a  concrete  dam  for  the  enlargement 
of  the  head  of  the  Louisville  and  Portland  Canal,1  comparison 
of  cost  of  hand  and  machine  mixing  is  given  by  Asst.  Engr.  J. 
H.  Casey. 

1.63  bbls.  natural  cemont,  at  $0.635  per  bbl.     .    .  $1.034 

2  volumes  sand,  .47  cu.  yd.,  at  .87  per  cu.  yd.  .    .  .408 

5  volumes  broken  stone,  .89,  cu.  yd.  at  $.84      .    .  .756 

Cost  of  testing  cement .081 

Forms,  material  for .107 

Forms,  labor  making  and  setting  up .168 

Cost  materials  and  forms $2.554 

Hand  mixed  concrete: 

.    Cost  of  mixing $1.917 

Cost  of  placing  and  tamping .791 

Cost  of  mixing  and  placing $2.708 

Total  cost  hand  mixed  concrete  per  cu. 

yd.  in  place $5.262 

Machine  mixed  concrete: 

Charging  and  running  mixer $0.864 

Placing  and  tamping .585 

Cost  mixing  and  placing $1.449 

Total  cost  machine  mixed  concrete  per 

cu.  yd.  in  place $4.003 

Difference  in  favor  machine  mixing $1.26 


1  Capt.  George  A.  Zinn,  Corps  of  Engineers,  U.  S.  A.,  in  charge. 
Chief  of  Engineers,  1900,  p.  3467. 


Report 


224 


CEMENT  AND  CONCRETE 


Since  the  above  concrete  was  placed  in  large  masses,  the 
costs  of  labor  are  considered  high,  and  it  is  probable  the  work 
was  done  with  exceptional  care. 

351.  In  the  construction  of  the  lock  at  the  Cascades  Canal1 
the  concrete  plant  was  so  arranged  that  the  materials  did  not 
have  to  be  elevated,  but  much  of  the  work  of  transportation 
was  done  by  gravity.  The  mixing  of  about  eighteen  hundred 
yards  by  hand  permits  a  comparison  to  be  made  with  machine 
mixing  by  which  method  about  seven  thousand  eight  hundred 
yards  were  made.  The  costs  were  as  follows: 


ITEMS. 

COST  PEH  Cu.  YD.  OF  CONCRETE. 

HAND  MIXED  AND 
PLACED  BY  DERRICK. 

MACHINE  MIXED  AND 
PLACED  BY  CHUTE. 

AMOUNTS. 

TOTAL. 

AMOUNTS. 

TOTAL. 

.805  bbl.    Portland  cement  at 
$4.08      .     . 

$3.20 
.47 
.60 

.54 
'.15 
.22 

$4.90 

.37 
1.09 
.79 

$3.29 
.47 
.60 

.54 
!l5 

.22 

'.39* 

.04 

141* 
.05 

$4.90 

.37 
.43 
.46 

.456  cu.  yd.  sand  at  $1.04     .     . 
.579  cu.  yd.  gravel  at  $1.04  .     . 
.317   cu.   yd.   broken  stone  at 
$1.70     
Cost  materials  in  concrete     . 
Timbering  . 

Testing    cement    and    general 
repairs  . 

Forms  and  tests  . 

Mixing,  labor 

1.07 
.02 

"        repairs  and  fuel  .     .     . 
Total  cost  mixing 

Placing,  labor 

.60 
.19 

"         fuel,  tramways,  etc. 
Total  cost  placing 

Total  cost  concrete  per  cu.  yd. 

. 

$7.15 

$6.16 

352.  In  the  construction  of  the  retaining  walls  for  the 
Chicago  Drainage  Canal,2  a  special  plant  was  designed  for  the 
work  on  account  of  the  large  quantities  of  concrete  required, 
and  this,  combined  with  the  low  cost  of  materials  and  the  char- 
acter of  the  work,  resulted  in  a  very  low  cost  concrete.  On 


1  Maj.  Thomas  H.  Handbury,  Corps  of  Engineers,  U.  S  .A.,  in  charge. 
Report    Lieut.  Edward  Burr,  Report  Chief  of  Engineers,  1891,  Vol.  v.     Ab- 
stracted, Engineering  News,  June  2,  1892. 

2  "  Construction  of  Retaining  Walls  for  the  Sanitary  District  of  Chicago," 
by  Mr.  James  W.   Beardsley,  and  discussion  by  Mr.  Charles  L.  Harrison. 
Jour.  W.  Soc.  Engrs.,  Dec.,  1898. 


EXAMPLES  OF  COST  225 

Section  14  the  stone  was  selected  from  the  spoil  banks  along  the 
canal  and  could  usually  be  obtained  within  one  hundred  feet. 
This  stone,  which  was  delivered  to  the  crusher  by  wheelbarrows, 
required  some  sledging  to  reduce  it  to  crusher  size.  An  Austin 
jaw  crusher  was  mounted  on  a  flat  car  with  the  Sooysmith 
mixer.  "The  cement,  sand  and  stone  were  raised  from  their 
respective  bins  by  means  of  belt  conveyors  running  at  the 
same  rate  of  speed,  but  carrying  buckets  spaced  proportional  to 
the  required  ingredients."  "The  cost  of  a  second  hand  plant 
used  on  this  section  was  estimated  at  $9,600,  including  two 
crushers  and  two  mixers  at  $1,500  for  each  machine.  Common 
labor  cost  $1.50  per  day;  firemen,  enginemen,  and  carpenters 
from  $2.00  to  $3.00  per  day.  The  itemized  cost  is  as  follows: 


ITEMS. 


COST,  CENTS 
PEK  CIT.YD. 


General,  including  superintendent,  blacksmith,  water  boys,  etc. 
Quarrying,  i.  e.,  delivering  stone  to  crusher 


Crushing 

Transportation,  delivering  sand  and  cement  to  mixer  by  teams 

Forms,  exclusive  of  lumber       

Mixing 

Placing  and  tamping 


7.8 
30.3 

7.3 
14.2 
15.0 
12.1 
10.8 


Total 

Cost  of  plant  (no  salvage  allowance) 
Cost  of  cement  and  sand    .... 
Total  cost  concrete  per  cubic  yard 


97.5 

40.7 

1(53.3 


33.015 


The  amount  of  concrete  used  on  this  section  was  23,568  cu.  yds. 
353.  On  Section  15  of  the  same  work  the  conditions  were 
somewhat  different.  The  stone  had  to  be  quarried  within  about 
a  thousand  feet  of  the  crusher.  The  stone,  after  being  broken 
to  crusher  size,  was  delivered  on  the  tipping  platform  of  the 
No.  7  Gates  crusher  in  cars  drawn  by  a  cable  hoist.  "The 
average  output  of  the  crusher  for  a  day  of  ten  hours  was  about 
210  cubic  yards."  The  materials  were  transported  to  the 
mixer  in  four  and  one-half  yard  dump  cars  drawn  by  a  light 
locomotive.  The  mixer  was  of  the  spiral  screw  type  and  de- 
posited the  materials  on  a  rubber  belt  conveyor.  The  mixer 
and  operating  machinery  were  mounted  on  a  car  which  pro- 
pelled itself  by  means  of  rope  and  winch.  The  plant  for  this 
section  was  new  and  estimated  to  cost  $25,420,  including  $12,000 
for  one  crusher. 


226  CEMENT  AND  CONCRETE 

The  detailed  cost  is  as  follows: 


ITEMS. 


COST 

PER  Cu.  YD.  OF 

CONCRETE, 

CENTS. 


General,  including  superintendent,  blacksmith,  teams,  etc. 
Quarrying  (exclusive  of  8.3  cents  for  explosives) 

Crushing 

Transportation,   delivering  cement,   sand    and  stone  on   a 

platform  beside  the  mixer 

Forms,  exclusive  of  timber 

Mixing,    including   shoveling    materials   from   platform   to 

mixer 

Placing  and  tamping 


Total 

Cost  of  plant  (no  salvage  allowance) 
Powder  for  quarrying  .... 
Cement  and  sand  . 


8.1 
14.2 

25.0 
11.6 


99.1 

50.7 

8.3 

158.6 


Total  cost  concrete  per  cu.  yd. 


$3.227 


The  amount  of  concrete  used  on  this  section  was  44,811 
cubic  yards. 


CHAPTER  XV 


THE  TENSILE  AND  ADHESIVE  STRENGTH  OF  CEMENT 
MORTARS   AND   THE   EFFECT  OF  VARIATIONS 
IN   TREATMENT    . 

ART.  45.     THE  TENSILE  STRENGTH  OF  MORTARS  OF  VARIOUS 
COMPOSITIONS  AND  AGES 

354.  THE  PROPORTION  OF  SAND.  — The  rate  of  change  in 
the  strength  of  mortars  as  the  proportion  of  sand  is  increased 
varies  greatly  for  different  cements.  The  fineness  and  chemical 
composition  of  the  cement,  and  the  quality  of  the  sand,  are  the 
most  important  factors  influencing  this  rate  of  change  upon 
which  the  question  of  the  relative  economies  of  different  mor- 
tars is  so  largely  dependent. 

Table  67  gives  the  results  of  tests  with  two  brands  of  Port- 
land cement  mixed  with  from  two  to  ten  parts  of  river  sand, 
the  age  of  briquets  being  six  months  and  two  years.  It  is  of 
interest  to  notice  that  the  strengths  of  the  mixtures  are  ap- 
proximately in  the  inverse  ratio  of  the  number  of  parts  of  sand 
used.  Thus  the  strength  with  six  parts  sand  is  approximately 
two-sixths  of  the  strength  with  two  parts,  while  with  ten  parts 
sand,  the  strength  is  nearly  two- tenths  of  that  with  mortar 
containing  two  parts. 

TABLE   67 

Rate  of  Decrease  in  Strength  with  Addition  of  Sand 
PORTLAND  CEMENT;  RIVER  SAND,   "  POINT  AUX  PINS  " 


TENSILE  STRENGTH,  LBS.  PEB  SQ.  IN. 

PARTS  SAND 

PROPORTIONATE 

TO  1 

CEMENT  BY 

6  MONTHS. 

2  YEARS. 

STRENGTH, 
Two  YEARS,  IF 

H 

R 

H 

R 

Mean. 

1  TO  2=100. 

2 

512 

504 

634 

548 

541 

100 

3 

390 

335 

363 

355 

359 

66 

4.09 

295 

261 

296 

288 

292 

54 

6 

175 

144 

191 

174 

182 

35 

8 

113 

96 

132 

132 

132 

24 

10 

(54 

74 

104 

116 

110 

20 

227 


-228 


CEMENT  AND  CONCRETE 


355.  In  Table  68  similar  results  are  given  for  two  samples 
of  Portland  cement  and  two  kinds  of  sand,  neat  cement  speci- 
mens being  included  in  the  comparison.  The  one-to-one  mor- 
tars give  a  higher  strength  than  neat  cement,  and  even  the 
mortar  containing  two  parts  of  the  limestone  screenings  is 
stronger  than  the  neat  specimens.  From  the  one-to-one  mor- 
tars the  strengths  decrease  rapidly  as  more  sand  is  added,  until 
five  parts  sand  are  used,  but  the  strengths  then  decrease  less 
rapidly  as  larger  additions  of  sand  are  made. 

TABLE   68 
Rate  of  Decrease  in  Strength  with  Addition  of  Sand 

PORTLAND  CEMENT,  BRAND  R;  SAND,  CRUSHED  QUARTZ  AND  LIMESTONE 

SCREENINGS 


TENSILE  STRENGTH,  POUNDS 
TEH  SQ.  IN. 

PROPORTIONATE 
STRENGTH  IK  STRENGTH 
1  TO  1  MOUTAR=  100. 

PARTS  SAND 

TO   1 

Sample        i 

Sample 

CEMENT  BY 

Cement  H  H, 

Cement  II, 

WEIGHT. 

Crushed  Quartz 

Limestone 

Crushed 

Limestone 

Sand,  20-30. 
Age  Briquets, 
G£  Months. 

Screenings,  20-30. 
Age  Briquets, 
6  Months. 

Quartz. 

Screenings. 

0 

689 

686 

82 

78 

1 

840 

881 

100 

100 

2 

521 

703 

62 

80 

3 

368 

508 

44 

58 

4 

236 

335 

28 

38 

5 

203 

267 

24 

30 

6 

156 

178 

19 

20 

8 

104 

138 

12 

15 

10 

78 

98 

9 

11 

356.  In  Table  69  two  samples  of  natural  cement  are  treated 
in  a  similar  manner,  from  one  to  eight  parts  river  sand  being 
used  in  the  mortars.     With  Sample  II  the  strength  is  dimin- 
ished rapidly  until  five  parts  sand  have  been  added,  but  with 
further  additions  of  sand,  the  strength  is  decreased  more  slowly. 
Sample   18  S  gives  quite  a  different  curve,  as   the   one-to-two 
mortar   is  stronger,  and  the  one-to-three  mortar    is  but  little 
weaker  than  the  one-to-one.     With  four  parts  sand  the  mortar 
shows  a  marked  falling  off  in  strength,  but  further   additions  of 
sand  diminish  the  strength  more  slowly. 

357.  INCREASE  IN  TENSILE  STRENGTH  WITH   TIME.  —  In 
Table  70  are  given  the  results  obtained  in  tests  of  tensile  strength 


COMPOSITION  AND  AGE 


229 


TABLE    69 

Rate    of    Decrease   in    Strength  with  Addition    of    Sand.     Natural 
Cement,  Brand  Gn;  River  Sand,  "Point  aux  Pins" 


TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

SAND  TO  1 
CEMENT 
BY  WKKJHT. 

AGE. 

6  MONTHS. 

2  YEARS. 

Proportionate 

Sample 
Cement 

II. 

188. 

18  S. 

Years  if  1   to  2 
r^lOO. 

0 

380 

1 

297 

308 

280 

86 

2 

200 

314 

324 

too 

3 

183 

280 

294 

91 

4 

128 

193 

187 

58 

5 

81 

101 

165 

51 

0 

69 

142 

172 

53 

7 

56 

119 

156 

48 

8 

53 

101 

114 

35 

with  twelve  samples  of  Portland  cement,  illustrating  the  rates 
of  increase  in  strength  from  seven  days  to  three  years.  It  is 
seen  that  rich  mortars  gain  strength  rapidly,  neat  and  one-to- 
one  mortars  showing  usually  eighty  to  ninety  per  cent,  of  their 
ultimate  strength  in  twenty-eight  days.  Mortars  containing 
not  more  than  four  parts  sand  to  one  cement  give  practically 
their  ultimate  strength  at  six  months.  It  is  also  of  interest  to 
notice  that  the  variations  in  strength  among  the  several  sam- 
ples are  not  very  great.  The  lowest  strength  at  the  end  of 
two  to  three  years  is  seventy-five  to  eighty  per  cent,  of  the 
highest. 

358.  In  the  case  of  natural  cements,  results  for  ten  brands 
of  which  are  given  in  Table  71,  only  fifty  to  seventy  per  cent, 
of  the  ultimate  strength  is  gained  in  the  first  twenty-eight 
days;  with  mortars  containing  three  parts  sand  to  one  cement 
the  average  result  at  twenty-eight  days  is  less  than  forty  per 
cent,  of  the  strength  at  two  years.  Most  of  the  samples  gain 
some  strength  after  six  months,  but  two  samples  fail  at  two 
years  which  had  given  a  fair  result  at  six  months.  The  varia- 
tions in  strength  among  the  several  samples  are  very  much 
greater  than  with  Portland  cements;  even  omitting  the  two 
samples  that  failed,  the  strength  of  the  highest  is  two  or  three 
times  the  strength  of  the  weakest  sample  at  two  years. 


230 


CEMENT  AND  CONCRETE 


Strength 


OF  SAND  TO  O 
BY  WEIGHT 


ONE  PART  SAND  TO  ON 
CEMENT  BY  WEIGHT. 


FINENESS: 
PER  CENT 
PASSING. 


£ 


•soui  9 


•soui  9 


•stop  82 


•soui  9 


COCOCOCOCOCOCOCO 


^<N,—  I 
COCOCO 


CO  GO 
(M  o 
(N  CO 


0  TfH  OU  CO  TC  O  O  rH  O  O  CO 

01  OS  GO  00  GO  t^-  t^-  tO  ^O  l^  CO 

cococococococococococo 


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CO^^t~^'—lt>. 
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•pirejg 


COMPOSITION  AND  AGE 


231 


o 


THREE  PARTS  SAND  T 
ONE  CEMENT. 


SAND 
ENT. 


Two  PA 
ONE 


E  PART  SAND 
CEMENT. 


•suuaX  z 


•soiu  9 


•sotu  g 


•stop  85 


•soui  9 


•stop  8S 


•stop 


•soui  9 


'SOU!   g 


•stop  82 


•stop 


•soui  9 


•stop 


•stop 


•top 


S 


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I-H  ;c  Ci  i~  00  CO  l^  -f  •?<«  CM  iO  Tfi  CO  1-1 
i—  i  CM  CO  W  rH  CN  CO  CO  CO  CM  CO  CM  T-H 


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7-4  QO  rn  "N  tS  O  '"  '-  «C  O  <M  QO  'N  t— 
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t-    0  CT.  Ci  CO 


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O^  O  O 


W    »V    W    VJV 

S^  CC  CC  T 


rH  >M  CO  <N  CO 


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't^c:ot-»-H'^cot-»o       o-^coco 


1-  CO  OS 


—  O 


232 


CEMENT  AND  CONCRETE 


359.  Table  72  shows  in  some  detail  the  rate  of  increase  in 
strength  of  a  sample  of  natural  cement  when  the  specimens 
are  maintained  in  air  and  in  water.  This  table  has  several 
points  of  interest.  When  hardened  in  water,  the  cement  gained 
steadily  in  strength  up  to  six  months,  when  it  began  to  fall 
off,  and  at  two  years  this  cement  failed,  as  is  shown  in  Table 
71.  The  neat  cement  specimens  hardened  in  air  are  very 
irregular,  as  usual.  These  specimens  showed  high  strength  at 
three  months,  suffered  a  marked  falling  off  at  six  months  and 
one  year,  but  showed  a  remarkable  strength,  equal  to  neat 
Portland  cement,  at  two  years.  The  strength  developed  at 
one  year  by  specimens  of  this  sample  containing  two  parts 
sand  to  one  cement  and  hardened  in  air,  is  also  equal  to  that 
shown  by  similar  mortars  of  Portland  cement. 

TABLE  72 

Rate  of  Increase  in  Strength  in  Water  and  Air 


AGE  OF  BRIQUETS. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

NEAT  CEMENT. 

MORTAR  Two  PARTS  SAND 
BY  WEIGHT  TO  ONE 
CEMENT. 

Water. 

Air. 

Water. 

Air. 

1  day   
7  days            .... 
14  days           .... 
28  days           .... 
3  raos.            .... 
6  mos.            .... 
1  year            .... 
2  years 

81 
192 
232 
305 
390 
437 
432 
395 

152 
254 
315 
473 
551 
372 
314 
731 

'  135  ' 

'  232  ' 
367 
409 
249 

'  142  ' 

271 
459 
475 

537 

All  cement,  Brand  Hn,  Sample  26  S,  which  fails  in  water  after  two  years, 
see  Table  71. 

ART.  46.     CONSISTENCY  OF  MORTAR  AND  AERATION  OF  CEMENT 

360.  EFFECT  OF  CONSISTENCY  OF  MORTAR  ON  TENSILE 
STRENGTH.  —  The  results  in  Table  73  are  from  briquets  of 
Portland  cement  with  two  parts  " Standard"  crushed  quartz. 
The  consistency  of  the  mortars  varied  from  a  "  trifle  dry/'  in 
which  water  rose  to  the  surface  only  after  continued  tamping, 
to  a  wet  mortar  which  would  just  hold  its  shape  when  placed 
in  a  heap  on  the  slab.  Half  of  the  briquets  were  immersed, 


CONSISTENCY 


233 


while  the  remainder  were  stored  in  the  air  of  the  laboratory. 
The  air  hardened  specimens  gave  higher  results  in  all  cases 
than  those  hardened  in  water.  The  highest  strength  was  given 
in  general  by  the  dryest  mortar,  but  the  differences  in  strength 
decrease  as  the  age  of  the  specimen  increases. 

TABLE    73 

Effect  of  Consistency  on  the  Strength  of  Portland  Cement  Mortar 
Hardened  in  Water  and  Air 


AGK  OK  BRIQUETS. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

Consistency  of  Mortar. 

Briquets  Hardened  in  Fresh 
Water. 

Briquets  Hardened  in  Air 
of  Laboratory. 

a 

b 

c 

(I 

e 

a 

b 

c 

d 

e 

7  days    .     .     . 

340 

310 

220 

101 

158 

407 

341 

263 

230 

202 

28  days    .     .     . 

883 

378 

314 

291 

240 

500 

463 

345 

393 

302 

3  months     .     . 

515 

535 

514 

429 

411 

065 

503 

638 

507 

451 

Cement:  Brand  R,  Sample  18  II,  with  two  parts  "Standard"  sand. 
Consistency:  a,  trifle  dry;  b,  O.K.;  c,  moist;  d,  very  moist;  e,  would  just 
hold  shape. 

361.  Tables  74  and  75  give  similar  results  for  Portland  and 
natural    cement    mortars,    respectively,    all    specimens    having 
hardened  in  water  for  three   months.     The   amount  of  water 
used  in  gaging  had  a  wide  range,  giving  mortars  of  all  consis- 
tencies from  very  dry  to  very  moist.     The  richness  of  the  mor- 
tar was  also  varied,  from  neat  cement  to  five  parts  sand.     A 
comparison  of  the  results  in  these  two  tables  indicates  that  the 
highest  strength  is  usually  given  by  mortars  a  trifle  dryer  than 
that  considered  right  for  briquets;  that  an  excess  of  water  is 
less  deleterious  to  rich  mortars  than  to  lean  ones,  and  to  Port- 
land cement  than  to  natural  cement, 

362.  Conclusions. —  Although  all  of  these  tests  indicate  the 
superiority  of  dry  mortars,  in  considering  the  effect  of  consis- 
tency from  a  practical  standpoint,  one  must  not  fail  to  consider 
the  difference  between  the  conditions  existing  in  the  actual  use 
of  mortars  and   in   laboratory  tests.     When  mortar  is  used  in 


234 


CEMENT  AND  CONCRETE 


TABLE    74 

Variations  in  Consistency  of  Mortar 
EFFECT  ON  STRENGTH  OF  PORTLAND  MORTAR  AT  THREE  MONTHS 


TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH,  FOR 

PARTS  SAND  TO 

CONSISTENCY  NUMBER. 

1  CEMENT 

BY  WEIGHT. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

0 

608 

635 

763 

744 

708 

707 

729 

085 

1 

513 

543 

618 

588 

594 

613 

566 

506 

538 

2 

429 

447 

398 

393 

382 

3 

289 

322 

329 

310 

279 

5 

.  .  . 

208 

.  .  . 

230 

201 

189 

167 

f  1  —  Very  dry  ;  little  or  no  moisture  appeared  on 
Consistency  —  surface  of  briquets. 

Significance  of  numbers  :     J   5  — About  proper  consistency  for  briquets. 
Increasing  per  cent,  water  |   9 _  Very  moist;  mortar  would  barely  hold  shape 
used  for  higher  numbers.    ^  and  shrank  in  molds  in  hardening. 


TABLE    75 

Variations  in  Consistency   of  Mortar 
EFFECT  ON  STRENGTH  OF  NATURAL  CEMENT  MORTAR  AT  THREE  MONTHS 


PARTS  SAND  TO 
1  CEMENT 
BY  WEIGHT. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH  FOR 
CONSISTENCY  NUMBER. 

1 

2 

3 

4 

5 

6 

7 

8 

9 

0 
1 

2 
3 
5 

.  .  . 

239 

372 
312 
255 
217 
150 

373 
314 

283 
208 
155 

'277' 
206 
125 

305 

286 
258 
183 
101 

281 
242 

268 
241 
204 
139 
74 

263 
207 
176 

.  .  . 

Consistency — Significance  of  numbers: 

1  — Very  dry;  little  or  no  moisture  appeared  on  surface  briquets. 
5  —  About  proper  consistency  for  briquets. 

9  —  Very   moist ;   mortar  would   barely  hold   shape  and   shrank  in 
hardening. 

masonry,  the  stones  or  bricks,  even  though  they  be  dipped, 
or  sprayed  with  a  hose  before  setting,  are  very  likely  to  press 
out  or  absorb  considerable  moisture  from  the  mortar.  To 
realize  this  one  has  only  to  raise  a  heavy  stone  just  after  it  has 
been  bedded;  and  the  greater  ease  of  setting  either  stone  or 


AERATION  OF  CEMENT 


231 


brick,  and  obtaining  a  full  mortar  bed,  with  a  rather  wet  mor- 
tar, is  appreciated  by  all  masons.  In  the  laying  of  concrete, 
the  difficulties  of  obtaining  a  compact  mass  with  a  dry  mortar  are 
also  not  to  be  overlooked,  but  this  point  is  discussed  elsewhere. 

363.  Effect  of  Aeration  on  the  Tensile  Strength  of  Cement.  - 
Portland  cements  that  are  not  perfect  in  composition  and 
burning,  and  that  therefore  contain  free  lime,  may  sometimes 
be  rendered  sound  by  exposing  them  to  air,  and  such  exposure 
was  at  one  time  considered  almost  essential  in  Portland  cement 
manufacture. 

Fresh  Portland  cements  that  are  slightly  defective  may  have 
their  properties  quite  radically  changed  by  such  treatment; 
their  rate  of  setting  becoming  first  more  rapid,  and  then,  by 
further  aeration,  slower,  and  their  tendency  to  expand  over- 
come or  ameliorated.  Portland  cements  that  are  perfectly 
sound  suffer  some  loss  in  specific  gravity  by  the  absorption  of 
carbonic  acid  and  water  from  the  atmosphere,  but  moderate 
aeration  has  no  radical  effect  upon  their  strength,  and  Port- 
lands deteriorate  but  very  slowly  by  storage,  provided  the 
cement  is  kept  dry  and  does  not  cake  in  the  package. 

Natural  cements,  however,  usually  suffer  by  aeration,  and 
this  is  illustrated  by  tests  on  several  samples  of  one  brand 
given  in  Tables  76  and  77.  Of  the  four  samples  in  Table  76, 

TABLE   76 
Effect  of  Aeration  on  Four  Samples  of  Same  Brand  Natural  Cement 


TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

NUMBER 

WEEKS 

CEMENT 

Age  of  Briquets,  6  Months  to  7  Months. 

Age  Briquets,  2  Years. 

AERATED. 

Sample  QQ 

ss 

NN 

OO 

NN 

OO 

0 

242 

183 

343 

340 

316 

306 

2 

237 

2(59 

357 

500 

368 

432 

5 

250 

403 

7 

268 

358 

. 

10 

. 

. 

225 

212 

246 

284 

11 

313 

279 

13 

.  .  . 

.  .  . 

213 

218 

200 

258 

Cement:  Brand  Gn;  Sand,  two  parts  crushed  quartz  to  one  cement. 
All  briquets  of  one  sample  were  made  by  one  molder  and  same  percentage 
water  used. 


236 


CEMENT  AND  CONCRETE 


NN  and  OO  showed  an  improvement  by  two  weeks'  exposure 
to  air,  spread  out  in  a  thin  layer,  but  longer  exposure  resulted 
in  a  serious  loss  of  strength.  Of  the  other  two  samples,  SS  was 
greatly  improved  by  five  weeks'  aeration,  but  longer  exposure 
was  detrimental,  while  sample  QQ  showed  a  continuous  im- 
provement up  to  the  limit  of  eleven  weeks'  exposure  to  air. 

In  Table  77  the  effect  of  aeration  on  five  samples  of  the  same 
brand  is  shown.  One  of  these  samples  was  overburned  and 
was  rendered  practically  worthless  by  fourteen  weeks'  exposure 
to  air.  Nearly  all  of  the  samples  in  this  table  were  seriously 
affected  by  six  weeks'  aeration. 

TABLE    77 

Natural  Cement.     Effect  of  Aeration 


TENSILE  STRENGTH,  POUNDS 

b 

CEMENT. 

PARTS 

PER  SQUARE  INCH,  CEMENT 

^  ° 

SAND 

AGE  OF 

AERATED. 

S£s£ 

TO  1 

BRI- 

u~gW 

CE- 
MENT. 

QUETS. 

a 

b 

SSfig 

02  «      0 

a 

Brand. 

Sam- 
ple. 

4  to  5 

days. 

11  to  12 
days. 

45  to  51 
days. 

99 
days. 

Gn 

84 

2 

6  ino. 

414 

321 

208 

216 

80.5 

54 

3.01 

" 

83 

' 

(t 

463 

392 

211 

235 

85.9 

41 

3.11 

t( 

82 

' 

" 

44o 

3oO 

217 

266 

8-3.6 

34 

3.09 

u 

U' 

' 

it 

383 

354 

273 

274 

87.8 

23 

2.95 

" 

0' 

' 

" 

203 

293 

277 

52 

89.7 

97 

3.14 

—  Fineness  expressed  as  per  cent,  passing  holes  .0046  inch  square. 

—  Time  setting  fresh  cement,  time  to  bear  Ta.j  inch  |  Ib.  wire. 

ART.  47.     REGAGING  CEMENT  MORTAR 


364.  The  Effect  of  Thorough  Gaging.  — The  value  of  thor- 
ough gaging  is  a  point  frequently  overlooked  in  the  preparation 
of  mortars  and  concretes.  Table  78  gives  a  few  of  the  results 
obtained  in  experiments  to  determine  the  effect  of  thorough 
work  in  mixing.  The  tests  are  made  with  two  brands  of  natural 
and  one  of  Portland ,  with  two  parts  sand  to  cne  cement  by 
weight.  The  two  minutes'  mixing  with  hoe  and  box  method 
gave  a  more  thorough  gaging  than  could  have  been  accom- 
plished in  the  same  time  with  a  trowel,  and  represented 
about  the  amount  of  work  put  on  mortars  for  testing.  We  are 
not,  therefore,  comparing  well  mixed  and  poorly  mixed  mortars, 
but  rather  well  gaged  and  better  gaged.  The  effect  of  the 
additional  work  is  shown  in  all  cases;  to  double  the  time  spent 


REGAGING 


237 


in  gaging,  increases  the  strength  of  the  resulting  mortar  about 
five  per  cent.,  while  to  quadruple  the  time  adds  twenty-six 
per  cent,  to  the  strength. 

TABLE   78 
Effect  of  Thorough  Gaging 


CEMENT. 

SAND,  Two  PARTS 
TO  ONE  CEMENT. 

TENSILE  STRENGTH,  LBS. 
FEU  So,.  IN.,  FOR  MORTAR 

REF. 

*       '   ' 

Kind. 

Brand. 

Kind  of  Sand. 

•2  Min. 

4  Min. 

8  Min. 

1 

Natural 

Gn 

j      Pt.  aux  Pins       J 
I     Pass  #10  Sieve     ) 

352 

350 

482 

2 

it 

it 

Standard 

418 

451) 

572 

3 

" 

An 

j      Pt.  aux  Pins       J 
I     Pass  #10  Sieve     j 

368 

376 

421 

4 

Portland 

R 

j      Pt.  aux  Pins        ) 
\     Pass  #10  Sieve     j 

625 

554 

010 

Mean   

416 

430 

523 

Prop 

ortional     ....                  

100 

105 

126 

365.  REGAGING.  —  When    more     mortar  is    mixed    at    one 
time  than  is  required   for   immediate   use,   there    is  always    a 
temptation  to   retemper  the  mass  and  use  it,  even  though  it 
may    have    been    standing    for    some   time.     The   practice    is 
usually   prohibited    by  specifications  and  strenuously   opposed 
by    engineers.      The  tests  recorded    in   Tables  79  to    83   were 
made    to    determine    the  effect   of  regaging    on  the  resulting 
strength  of  the  mortar. 

366.  The  results  obtained  with  two  brands  of  Portland  ce- 
ment are  given  in  Table  79.     The  first  result  in  each  line  of  the 
table  is  the  strength  attained  by  the  mortar  when  treated  as 
usual.     The  severity  of  the  treatment  of  the  mortar  as  regards 
regaging  is  shown  by  the  letters  heading  the  columns  and  the 
corresponding  foot  notes.     The  first  general  statement  to  be 
made  concerning  the  results  in  this  table  is  that  in  no  case  is 
the  effect  of  regaging  Portland  mortars  containing  sand  shown 
to  be  seriously  deleterious  to  the  tensile  strength.     Neat  cement 
mortar  is  not  improved  by  regaging,  and  if  allowed  to  stand 
more  than  one  hour,  and  then  made  into  briquets  without  any 
further  addition  of  water,  the  strength  is  considerably  decreased. 
If  water  is  added  and  the  mortar  frequently  regaged,  however, 


238 


CEMENT  AND  CONCRETE 


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REGAGINO 


239 


even  neat  cement  mortar  does  not  suffer  a  great  decrease  in 
strength  by  three  to  six  hours  standing.  Rich  mortars,  con- 
taining one  part  sand,  are  not  seriously  affected  by  standing 
three  hours  if  regaged  frequently.  Poorer  mortars,  with  two 
to  four  parts  sand,  show  an  actual  increase  in  strength  as  the 
effect  of  such  severe  treatment  as  standing  five  hours,  if  re- 
tempered  with  more  water  once  an  hour.  These  two  brands 
were  slow  setting  Portlands,  beginning  to  set  in  forty  minutes 
to  two  hours.  The  increase  in  strength  of  the  regaged  mortars 
is  doubtless  due,  at  least  in  part,  to  the  more  thorough  gaging 
which  they  received. 

Table  80  gives  similar  results  of  briquets  one  year  old  made 
at  another  time  with  two  parts  river  sand.  The  fact  that  dur- 
ing the  delay  between  the  making  and  use  of  the  mortar  it 
should  be  frequently  retempered  with  water  to  make  up  for 
the  loss  by  evaporation,  is  plainly  shown. 

TABLE  80 
Regaging  Portland  Cement  Mortar 


TKNHIMS  STKKNGTH,  POUNDS  PKR  SQUARK  INCH,  FOR  VARYING  TRKATMKNT. 

a 

c 

d 

e 

/ 

h 

i 

j 

579 

565 

5(39 

570 

568 

.  .   . 

•  .  . 

554 

579 

.  .  . 

.   .   . 

.  .  . 

627 

624 

560 

Cement:  Portland,  Brand  R,  Sample  42  M.    Sand:  2  parts  "  Point  aux 
Pins  "  passing  No.  10  sieve.     Age  of  briquets.  1  year. 
Treatment:  —  a  —  Molded  as  soon  as  gaged. 

c  —  Mortar  let  stand  1  hour,  regaged  and  briquets  made. 

d  —  Mortar  let  stand  3  hours,  regaged  each  hour. 

h  —  Mortar  let  stand  3  hours,   regaged  each  hour  and  water 

added  to  restore  original   consistency. 
e  —  Mortar  let  stand  5  hours,  regaged  each  hour. 
i  —  Mortar  let  stand  5  hours,  regaged  each  hour  and  water 

added  to  restore  original  consistency. 

/  —  Mortar  let  stand  5  hours,  regaged  and  briquets  made. 
/  —  Mortar  let  stand   5  hours,   regaged  and  briquets  made ; 
water  added  to  restore  original  consistency. 

367.  Similar  tests  with  natural  cements  are  shown  in  Table 
81,  and  it  appears  that  cements  of  this  class,  especially  if  mixed 
neat,  will  not  stand  the  same  severe  treatments  without  injury. 


240 


CEMENT  AND  CONCRETE 


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242 


CEMENT  AND  CONCRETE 


Neat  cement  mortars  of  these  two  brands  appeared  more  plastic 
when  they  were  retempered  with  more  water  after  standing  one 
hour  (column  /),  but  if  allowed  to  stand  three  hours  (column 
i)t  they  had  then  become  quite  hard  set.  Mortars  containing 
two  parts  sand  that  had  stood  sixty  to  ninety  minutes  with 
intermediate  retempering,  showed  a  slight' increase  in  tensile 
strength,  but  more  severe  treatment  was  deleterious. 

In  Table  82  the  mortars  all  contain  two  parts  sand  to  one 
of  cement  by  weight.  The  only  cases  of  any  serious  results  of 
retempering  are  for  mortars  standing  four  hours  and  regaged, 
at  intervals  of  one-half  hour  or  one  hour,  with  no  water  added 
to  th3  original  mortar.  Briquets  made  from  mortar  that  had 
been  gaged  every  half  hour,  and  was  molded  two  hours  after 
first  mixed,  showed  a  somewhat  higher  strength  than  briquets 
made  of  fresh  mortar. 

Table  83  shows  that  the  behavior  of  regaged  natural  cement 
mortars,  as  shown  in  the  preceding  tables,  is  not  an  eccentricity 
of  one  or  two  brands.  Mortars  containing  two  parts  sand  do 
not  appear  to  suffer  in  tensile  strength  by  being  allowed  to 
stand  two  hours  if  regaged  hourly. 

TABLE   83 

Effect  of    Regaging    on    Tensile    Strength,    Five    Brands    Natural 

Cement 


o 

« 

TENSILE  STRENGTH,  POUNDS  PER 

H    ^ 

AGE 
BRIQUETS. 

TIME 
ELAPSED 

BETWEEN 

FIRST  GAG- 

L NtTMBE 
LGINGS. 

INTERVAL 
BETWEEN 

SUC- 
CESSIVE 

SQUARE  INCH. 

BRANDS. 

IS 

ING  AND 
MOLDING. 

H^ 

GAGINGS. 

H 

En 

An 

Dn 

Kn 

Hn 

04 

2 

28  days 

1 

58 

171 

231 

178 

174 

2 

it 

2  hours 

3 

1  hour 

109 

168 

310 

178 

190 

2 

6  months 

1 

228 

3*8 

306 

361 

273 

2 

" 

2  hours 

3 

1  hour 

284 

382 

307 

416 

347 

4 

28  days 

1 

39 

49 

149 

23 

58 

4 

tt 

2  hours 

3 

1  hour 

33 

70 

146 

56 

4 

6  months 

1 

104 

146 

188 

'216 

129 

4 

" 

2  hours 

3 

1  hour 

97 

147 

184 

227 

137 

NOTES:  — Sand,  Point  aux  Pins,  passing  No.  10  sieve. 
In  general,  each  result  mean  of  five  briquets. 
All  briquets  made  by  one  molder  and  stored  in  one  tank. 
All  mortars  appeared  about  same  consistency  when  molded. 
No  water  added  in  regaging  except  Brand  Kn,  1  to  2  mortar, 
standing  two  hours. 


MIXING  CEMENTS  243 

368.  Conclusions.  —  The  conclusions  to  be  drawn  from  these 
tests  appear  to  be  as  follows:  The  cohesive  strength  of  mortars 
of  neat  cement  is  appreciably  diminished  if  they  are  allowed  to 
stand  a  considerable  length  of  time  after  gaging  before  they 
are  used.     Sand  mortars,  especially  of  Portland  cement,  usually 
develop  a  higher  tensile  strength  under  moderate  treatment  of 
this  kind;  and  if  regaged  frequently,  with  sufficient  water  added 
to  keep  them  plastic,  mortars  of  slow  setting  cements  may  be 
used  several  hours  after  made  without  serious  detriment  to  the 
tensile  strength.     Portland  cements  withstand  severe  treatment 
better  than  natural  cements. 

The  effect  of  regaging  on  the  adhesive  strength  is  shown  in 
Table  117,  §  405.  These  tests  were  quite  severe  and  pointed  to 
the  conclusion  that  the  adhesive  strength  is  diminished  by  stand- 
ing and  regaging,  rich  mortars  and  natural  cement  mortars 
being  most  affected. 

The  effect  of  regaging  on  a  given  sample  should  be  investi- 
gated before  it  is  permitted  to  any  great  extent,  or  in  the  most 
careful  work.  Regaged  mortars  are  said  not  to  give  good  re- 
sults in  sea  water,  and  it  may  be  expected  that  quick  setting 
cement  will  be  injured  by  regaging. 

ART.  48.     MIXTURE  OF  CEMENT  WITH  LIME,  ETC. 

369.  Mixture  of  Portland  and  Natural  Cements.  —  For  cer- 
tain uses  mortar  is  sometimes  made  from  a  mixture  of  Portland 
and  natural  cement,  with  the  idea  of  retaining  some  of  the 
properties  of  the  Portland   without  involving  the  expense  of 
using  a  clear  Portland  mortar.     Several  tests  have  been  made 
to  determine  the  rate  of    hardening  and  the  ultimate  strength 
of  such  mixtures. 

The  mortars  used  in  the  tests  given  in  Table  84  contained  two 
parts  sand  to  one  of  cement,  and  the  cement  was  composed  of 
one-eighth,  one-quarter  and  one-half  Portland  to  seven-eighths, 
three-quarters,  and  one-half  natural.  Mortars  made  with  Port- 
land alone  and  with  natural  alone  are  included  for  comparison. 
It  is  seen  that  the  mortars  containing  some  Portland  harden 
more  rapidly  than  the  natural  cement  mortar,  so  that  the  in- 
creased strength  developed  at  short  periods  is  more  than  pro- 
portional to  the  per  cent,  of  Portland  used.  The  results  ob- 


244 


CEMENT  AND  CONCRETE 


tained  at  two  and  three  years,  however,  indicate  that  mortars 
containing  only  a  small  proportion  of  Portland,  as  one-eighth 
or  one-quarter,  do  not  give  a  higher  ultimate  strength  than  is 
obtained  with  clear  natural  cement  mortar. 

TABLE   84 

Tensile  Strength  of  Mortars  Made  with  Mixture  of   Portland  and 

Natural 


w 

o 
g 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

ti 

BRIQUETS. 

Per    I  Portland 

100 

50 

25 

12.5 

0 

a 

Cent.  (  Natural 

00 

50 

75 

87.5 

100 

i 

7  days 

291 

205 

108 

75 

24 

2 

28  days 

357 

264 

219 

190 

123 

3 

0  months 

550 

425 

378 

300 

322 

4 

1  year 

. 

574 

441 

360 

336 

291 

5 

2  years 

543 

449 

375 

343 

393 

0 

3  years 

592 

501 

428 

370 

429 

NOTES.  —  Portland  cement,  Brand  R,  Sample  42  M. 
Natural  cement,  Brand  Gn,  Sample  54  R. 
Sand,  two  parts  of  "  Point  aux  Pins,"  pass  No.  10  sieve,  to  one 

part  cement  by  weight. 

All  briquets  made  by  one  molder  and  immersed  in  one  tank. 
Each  result,  mean  of  ten  briquets. 

370.    In    Table   85   four  kmds   or   mixtures   of    cement   are 
used,  Portland,  natural,  an  " Improved   cement"  or  a  cement 

TABLE   85 

Comparisons  of  Portland,  Natural,  and  "  Improved  "  Cements 


§c% 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

H  •<  ^  £  S 

AGE  OF 

REF. 

2||S| 

WHEN 

BROKEN. 

Portland, 
Brand  U. 

"  Improved," 
Brand  Nn. 

Portland,20%, 
Natural,  80%. 

Natural, 
Brand,  Mn. 

1 

None 

7  days 

547 

206 

250 

199 

2 

it 

28      " 

586 

293 

341 

270 

3 

One 

7     " 

458 

169 

200 

165 

4 

u 

28     " 

569 

253 

331 

234 

5 

1C 

7  months 

702 

550 

578 

517 

6 

" 

2  years 

577 

563 

534 

497 

7 

Two 

2      " 

522 

510 

573 

529 

8 

Three 

7  days 

176 

52 

80 

49 

9 

it 

28     " 

272 

122 

143 

114 

10 

u 

6£  months 

389 

301 

282 

255 

11 

(f 

2  years 

371 

346 

356 

342 

12 

Mean 

2  years 

490 

473 

488 

456 

LIME  WITH    CEMENT  1M5 

sold  as  a  mixed  cement,  and  a  sample  made  by  mixing  twenty 
per  cent,  of  the  Portland  with  eighty  per  cent,  of  the  natural. 
The  first  point  noticed  is  that  the  " Improved"  cement  does 
not  exhibit  the  early  hardening  properties  due  to  the  Portland 
cement  in  its  composition  (if  any),  as  strongly  as  the  sample 
containing  twenty  per  cent.  Portland.  In  only  two  tests  did 
the  "Improved"  cement  give  a  higher  strength  than  the  clear 
natural.  The  results  of  the  two-year  tests  are  of  interest  as 
showing  how  nearly  the  same  ultimate  strength  is  shown  by 
the  four  samples.  The  sample  of  natural  cement  is  of  excep- 
tional quality. 

371.  Conclusions.  —  It  appears  from  these  tests  on  the  effect 
of  mixing  Portland  and  natural  cements  that,  in  general,  the 
full  strength  of  both  cements  is  developed  in  the  mixture;  that 
in  the  early  stages  of  hardening,  the  mixture  sometimes  ex- 
hibits   more    nearly    the    properties    of    the    Portland,    gaining 
strength  quite  rapidly,  but  that  the  ultimate  strength  of  mix- 
tures containing  small  amounts  of  Portland  are  sometimes  as 
low  as  mortars  made  with  natural  cement  alone.     It  cannot  be 
stated  that  all  samples  of  Portland  and   natural  cement   will 
give  as  good  results  in  combination  as  those  obtained  in  the 
above  tests,  and  any  extended  use  of  such  mixtures  should  be 
based  on  full  tests  of  mixtures  of  the  brands  that  are  to  be  used 
in  combination. 

372.  Free  Lime  in  Cement.  —  The  presence  of  free  lime  in 
cement  is  known  to  be  a  serious  defect.     Table  86  gives  the 
results  obtained  by  adding  ground  quicklime  to  Portland  cement 
in  one-to-two  mortars.     It  appears  that  eight  per  cent,  quick- 
lime reduces  the  strength  at  six  months  about  twenty-five  per 
cent.,   and    smaller    amounts    of    lime    produce    approximately 
proportional     decrements.      The    seven-day   results,    both   hot 
and   cold,   show  greater   proportional   effects.      The   free   lime 
occurring  in   cements   as  a  result  of  defects  of   manufacture  is 
likely  to  be   much  more  dangerous  in  character  than  the  lime 
used  in  these  tests. 

373.  THE  USE  OF  SLAKED  LIME  WITH  CEMENT.  —  A  small 

quantity  of  Portland  cement  is  frequently  added  to  lime  mortar 
to  hasten  the  hardening  and  improve  the  strength.  The  ad- 
dition of  a  small  amount  of  slaked  lime  to  Portland  cement 
mortar  is  also  practiced.  This  not  only  cheapens  the  mortar 


246 


CEMENT  AND  CONCRETE! 


TABLE    86 
Mixture  of  Ground  Quicklime  with  Portland  Cement 


BRIQUETS  STORED 
IN  WATER. 

AGE  OF 
BRIQUETS. 

TENSILE  STRENGTH  OF  MORTARS  IN 
POUNDS  PER  SQUARE  INCH. 

Lime  as  Per  Cent,  of  Total  Lime  and  Cement. 

0 

2 

4 

6 

8 

Hot  80°  C.  .     .  '  .     . 
Hot  80°  C  
Ordinary  tank 
Ordinary  tank 

3  days 

7  days 
7  days 
6  months 

269 
367 

348 
604 

223 

297 
321 
545 

207 
266 
273 
489 

194 
223 
241 
495 

159 
191 
220 
454 

NOTES.— Cement:  Portland,  Brand  R,  Sample  83  T. 

Lime:  Quicklime   ground  to  pass   No.   100  sieve  (holes  .0065 

in.  sq.). 
Sand:   Standard  crushed   quartz,  600  grams,  to  300  grams  of 

cement  plus  lime. 
Per  cent,  of  lime  given  replaced  the  same  weight  of  cement; 

thus:  for  "4  per  cent,  lime"  the  mortar  contained  288  grams 

cement,  12  grams  lime  and  600  grams  sand. 
All  briquets  made  by  one  molder;  each  result,  mean  of  five 

briquets. 

but  renders  it  much  more  plastic,  or  less  "  brash,"  in  mason's 
parlance.  It  is  very  difficult  to  lay  bricks  in  a  full  mortar  bed 
with  Portland  cement  mortar  containing  two  or  three  parts 
sand  to  one  cement,  and  to  use  a  richer  mortar  is  usually  too 
expensive.  The  work  is  very  much  facilitated  by  mixing  a 
little  slaked  lime  paste  or  powder  with  the  mortar. 

374.  The  tensile  strength  of  such  mixtures  is  shown  by  the 
tests  in  Tables  87  to  89.  In  the  mortars  of  Table  87  a  sample 
of  Portland  cement  is  mixed  with  slaked  lime  in  two  forms, 
paste  and  powder.  When  the  briquets  are  hardened  in  open 
air  the  addition  of  ten  to  twenty  per  cent,  of  CaO  in  the  form 
of  lime  paste  decreases  the  strength  about  twenty-five  per  cent. ; 
seven  per  cent,  of  lime  in  the  form  of  slaked,  dry  powder  has, 
however,  no  deleterious  effect,  and  even  twenty-eight  per  cent, 
gives  no  serious  decrease  in  strength.  For  water-hardened 
specimens  the  addition  of  twenty  to  thirty  per  cent,  of  lime  in 
the  form  of  paste  appears  to  increase  the  strength  twenty  per 
cent,  and  no  deleterious  effect  is  shown  by  the  addition  of 
forty  per  cent.  Also  for  water-hardened  specimens,  seven  to 


LIME   WITH  CEMENT 


247 


twenty-eight  per  cent,  of  CaO  in  the  form  of  slaked  powder  in- 
creases the  strength  nearly  twenty  per  cent.  It  thus  appears 
that  the  addition  of  lime  gives  better  results  in  mortars  that  are 
to  harden  in  water,  and  that  for  air-hardened  mortars  lime 
powder  should  be  used  in  preference  to  lime  paste.  Similar 
tests  of  seven-day  briquets  showed  the  lime  paste  to  retard 
the  hardening  of  the  mortar. 

TABLE  87 

Slaked  Lime  in  Portland  Cement  Mortars 


TKXSILK  STRENGTH, 

PROPORTIONS. 

Poi'XUS   PER 

SQUARE  INCH.,  SAMPLE 

STORED  IN 

RKF. 

Li  MR   IN    FOIIM 
OF 

CaO  in  Lime 

Cement, 
Grains. 

Paste  or 
Powder, 

Saml, 
Grams. 

Open  Air. 

Water 

Laboratory. 

Grains. 

1 

Paste 

200 

0 

600 

404 

382 

2 

200 

20 

000 

308 

426 

3 

200 

40 

600 

292 

450 

4 

200 

60 

000 

224 

462 

5 

200 

80 

600 

219 

384 

0 

Powder 

200 

0 

000 

382 

371 

7 

200 

14.3 

600 

385 

443 

8 

200 

28.6 

000 

316 

451 

9' 

200 

42.8 

600 

338 

431 

10 

200 

•      57.1 

600 

325 

440 

Cement:  Portland,  Brand  R.  Sand:  Crushed  Quartz,  20-30,  or  "Standard." 
Age  of  briquets,  6  months. 

375.  In  Table  88  only  lime  paste  is  used,  but  both  Portland 
and  natural  cement  are  tested,  and  the  specimens  are  hardened 
in  dry  air  and  damp  sand.  In  the  first  column  of  results 
are  given  the  strengths  attained  by  Portland  cement  mortar 
containing  three  parts  sand  to  one  of  cement  without  lime. 
In  the  second  column,  ten  per  cent.  CaO  in  form  of  paste  is 
added  to  the  cement.  In  the  third,  fourth  and  fifth  columns, 
respectively,  ten,  twenty-five  and  fifty  per  cent,  of  the  cement 
is  replaced  by  CaO. 

It  appears  that  ten  per  cent,  of  the  cement  in  a  one-to- 
three  Portland  mortar  may  be  replaced  by  lime  made  into  paste 
without  diminishing  the  strength,  if  the  mortar  hardens  in 
damp  sand.  Even  in  dry  air  exposure,  it  is  only  at  one  year 


248 


CEMENT  AND  CONCRETE 


that  the  lime  shows  any  deleterious  effect.  To  replace  twenty- 
five  per  cent,  or  more  of  the  cement  with  lime,  however,  dimin- 
ishes the  strength  of  the  mortar  in  a  marked  degree. 

In  the  case  of  natural  cement,  replacing  ten  per  cent,  of  the 
cement  with  lime  is  decidedly  beneficial,  and  even  twenty- 
five  per  cent,  lime  gives  enhanced  strength,  except  for  speci- 
mens hardened  in  dry  air. 

Table  89  gives  similar  results  for  one-to-four  mortars  and 
different  percentages  of  lime,  the  briquets  being  hardened  in 
dry  air  and  damp  sand. 

TABLE   88 

Use   of  Lime   Paste   in   Cement   Mortars    Containing    Three    Parts 

Sand 


TENSILE  STRENGTH,  LBS.  PER  SQ.  IN. 

Cement,     gm. 

200 

200 

180 

150 

100 

FERENCE. 

CEMENT. 

• 

BRIQUETS 
STOKED. 

AGE 

BIQUETS. 

GO 

300 

Lime  Paste,  " 

0 

60 

150 

CaO  in  Lime 
Paste,  gin. 

0 

20 

20 

50 

100 

a 

PQ 

Amt.  CaO  ex-") 

pressed  as  %  [ 
of  Cement  f 

0 

9 

10 

25 

50 

nln«  T  imp    1 

Kind. 

Brand 

plus  .Ljllliu.j 

600 

Sand,  gm. 

600 

600 

600 

600 

i 

Port. 

X 

Dry  aii- 

28  da. 

201 

242 

238 

168 

57 

2 

Damp  sand 

(i 

294 

330 

309 

238 

95 

8 

Dry  air 

3  uio. 

236 

205 

264 

171 

70 

4 

Damp  sand 

u 

350 

410 

398 

309 

125 

6 

Dry  air 

l  yr. 

384 

377 

317 

215 

98 

6 

Damp  sand 

(( 

430 

445 

442 

332 

171 

7 

Nat. 

An 

Dry  air 

3  mo. 

310 

338 

359 

251 

69 

8 

Damp  sand 

u 

267 

344 

327 

318 

93 

9 

Water 

(( 

222 

301 

319 

293 

79 

In  all  of  the  above  tests  the  mortars  containing  much  lime 
paste  were  not  only  more  plastic,  but  somewhat  wetter  than 
the  corresponding  mortars  of  cement  and  sand  alone,  on  ac- 
count of  the  water  contained  in  the  paste. 

376.  The  conclusion  to  be  drawn  from  these  tests  appears 
to  be  that  the  addition  of  a  small  amount,  ten  to  twenty  per 
cent.,  of  slaked  lime  to  cement  mortars  containing  as  much  as 
three  parts  sand,  not  only  renders  them  more  plastic,  but 
actually  increases  the  tensile  strength,  especially  if  the  mortars 
are  kept  damp  during  the  hardening.  It  also  appears  that  for 


PLASTER  PARIS   WITH  CEMENT 


249 


TABLE   89 

Use    of    Lime    Paste    in    Cement    Mortars    Containing  Four   Parts 
Sand  to  One  Cement 


COMPOSITION  OF  MORTAR. 

TENSILE  STRENGTH  OF  MORTAR, 
POUNDS  PER  SQUARE  INCH. 

Cement. 

Lime 
P't^te 

Lime 
in 

Sand, 

Stored  in  Damp 
Sand. 

Stored  in  Dry 
Air. 

Paste, 

Grams. 

Fresh 

Old 

Fresh 

Old 

Kind. 

Grams. 

Grams. 

Lime 

Lime 

Lime 

Lime 

Paste. 

Paste. 

Paste. 

Paste. 

Portland,   \ 

240 

00 

00 

960 

170 

180 

254 

244 

Brand  X,   1 

240 

80 

27 

900 

212 

200 

280 

250 

Sample      1 

200 

120 

40 

900 

198 

212 

227 

237 

41  S        I 

180 

180 

00 

960 

204 

194 

232 

184 

Natural, 
BrandAn,  4 
Sample  L   (^ 

240 
240 
200 
180 

00 

80 
120 

180 

00 
27 
40 
00 

960 
900 
900 
960 

150 
160 
160 
140 

133 

154 
173 
166 

127 
162 
131 
124 

142 
150 
170 
154 

NOTE. — All  briquets  three  months  old  when  broken. 

mortars  exposed  to  the  open  air  the  lime  should  be  in  the  form 
of  slaked  powder  rather  than  paste.  It  may  be  added,  that  in 
all  cases  care  should  be  taken  that  the  lime  is  thoroughly  slaked 
before  use,  and  all  lumps  should  be  removed  by  straining  or 
sifting.  Further  results  on  this  subject  are  given  in  connection 
with  the  tests  on  adhesion  of  cement  mortar  to  brick  (Art.  5). 

377.  EFFECT  OF  PLASTER  OF  PARIS  ON  THE  COHESIVE 
STRENGTH  OF  MORTARS. 

The  use  of  plaster  of  Paris,  or  calcium  sulphate,  in  the  man- 
ufacture of  cement  to  regulate  the  time  of  setting,  has  already 
been  mentioned.  The  amount  of  such  additions  at  the  factory 
are  usually  small,  the  German  Cement  Makers'  Association  limit- 
ing it  to  two  per  cent. 

Tests  on  three  brands  of  Portland  cement,  showing  the  effect 
of  small  additions  of  plaster  Paris,  are  given  in  Table  90.  All 
of  these  mortars  hardened  in  water.  It  is  not  known  whether 
any  of  the  cements  had  received  additions  of  plaster  Paris  be- 
fore leaving  the  factory.  It  is  probable  that  brands  R  and  X 
had  been  so  treated,  since  they  are  German  cements,  but  it  is 
not  probable  that  the  other  brands  of  Portland  had  received 
any  addition  of  plaster. 

It  appears  that  with  these  brands  the  addition  of  from  one 


250 


CEMENT  AND  CONCRETE 


to  three  per  cent,  of  plaster  Paris  hastens  the  hardening  and 
increases  the  strength  of  the  mortar  at  ages  of  six  months  to 
two  years.  Six:  per  cent,  plaster  sensibly  retards  the  hardening, 
but,  in  all  cases  except  one,  Brand  S,  neat,  six  months,  the 
mortars  containing  six  per  cent,  plaster,  gave  higher  results 
on  long  time  tests  than  did  the  corresponding  mortars  to  which 
no  plaster  had  been  added. 

TABLE    90 

Plaster  of  Paris  in  Portland  Cement  Mortars,  Hardening  in  Water 


ft* 

OH. 

TENSILE  STRENGTH,  POUNDS  PER  SQ. 

1 

fig 

§jj 

TEMPERA- 
TURE WATER 

IN  WHICH 

m 

IN.,  WITH  PER  CENT.  OF  CEMENT 
KEPLACED  BY  PLASTER 
OF  PARIS. 

w 
S 

Sg 

"H 

BRIQUETS 

^DS 

d 

s* 

§  ^ 

STORED. 

M 

r>  H^ 

^  ^ 

PH 

0 

l 

2 

3 

6 

GO 

PP 

1 

S 

0 

60°to65°Fahr. 

7  da. 

487 

626 

600 

519 

380 

2 

0 

6  mos. 

743 

746 

754 

742 

660 

3 

2 

7  da. 

323 

388 

360 

289 

182 

4 

2 

6  mos. 

492 

530 

547 

607 

663 

5 

2 

lyr. 

487 

515 

610 

588 

647 

6 

2 

2yrs. 

533 

586 

612 

659 

684 

7 

R 

0 

7  da. 

562 

608 

726 

709 

432 

8 

0 

6  mos. 

745 

751 

799 

804 

795 

9 

2 

7  da. 

288 

347 

372 

352 

165 

10 

2 

6  mos. 

532 

538 

624 

638 

642 

11 

2 

lyr. 

591 

595 

643 

645 

666 

12 

2 

2yrs. 

590 

623 

680 

673 

666 

13 

X 

0 

7  da. 

351 

368 

405 

450 

204 

14 

0 

6  mos. 

560 

606 

580 

645 

797 

15 

2 

7  da. 

227 

258 

261 

282 

96 

16 

2 

6  mos. 

494 

54(5 

591 

574 

563 

17 

2 

lyr. 

•572 

580 

586 

583 

652 

18 

2 

2  yrs. 

592 

575 

592 

592 

667 

19 

S 

2 

176°  Fahr. 

5  da. 

296 

307 

362 

391 

422 

20 

R 

2 

140°   " 

5  da. 

403 

440 

416 

495 

442 

21 

X 

2 

140°   " 

5  da. 

361 

334 

•  390 

452 

474 

NOTES.  —  Sand,  Point  aux  Pins  (river  sand)  passing  No.  10  sieve,  except 
for  hot  tests,  where  standard  sand  was  used.  Cement  and 
plaster  of  Paris  passed  through  No.  50  sieve  before  using. 
Plaster  Paris  had  no  apparent  effect  on  consistency  mor- 
tar at  first,  but  after  making  first  three  briquets  of  batch 
of  five,  the  mortar  containing  plaster  Paris  dried  out 
somewhat. 
Each  result,  mean  of  five  briquets. 

Similar  tests  of  natural  cement  mortars  hardening  in  water 
are  given  in  Table  91.     One  of  the  brands  is  not  much  affected 


PLASTER  PARIS  WITH  CEMENT 


L>51 


TABLE  91 
Plaster  of  Paris  in  Natural  Cement   Mortars,  Hardening   in  Water 


TENSILE  STRENGTH,  POUNDS  PER 

CEMENT, 

SAND, 

TEMPER- 

AGE OF 

SQUARE  INCH,  WITH  PEII  CENT. 
OF  CEMENT  REPLACED  BY- 

REF. 

NATURAL 
BRAND. 

PARTS  TO 
ONE 
CEMENT. 

ATURE 
WATER 
WHERE 
STORED. 

BRIQUETS 
WHEN- 
BROKEN. 

PLASTER  OF  PARIS. 

0 

1 

2 

3 

6 

Degrees  F. 

1 

An 

0 

00-65 

7  da. 

23:} 

225 

213 

235 

a 

2 

0 

0  mo. 

422 

449 

438 

441 

324 

3 

2 

7  da. 

111 

109 

97 

144 

a 

4 

2 

6  mo. 

418 

416 

435 

409 

133c 

5 

2 

1  yr. 

415 

451 

430 

454 

0 

2 

2  yrs. 

478 

476 

489 

514 

7 

Gi 

0 

7  da. 

146 

156 

115c 

a 

a 

8 

0 

6  mo. 

383 

3986 

323 

312e 

234/ 

9 

2 

7  da. 

62 

80 

94 

a 

a 

10 

2 

0  mo. 

374 

312 

355 

86/ 

161/ 

11 

2 

l  yr. 

448 

395 

408 

131/ 

107/ 

12 

2 

2  yrs. 

456 

437 

397 

172/ 

a 

13 

An 

2 

140 

5  da. 

310 

365 

405 

402 

203 

14 

Gii 

2 

4  . 

.  i 

359 

351 

189 

138 

100 

NOTE.  —  Sand,  Point  aux   Pins  (river  sand)  passing   No.  10  sieve,  ex- 
cept for  hot  tests,  where  standard  sand  was  used. 
a  —  Found  badly  swelled  and  nearly  disintegrated  after  a  few 

days  in  tank. 

6  —  Surface  cracks,  1  inch  section  swelled  to  1  ^  inches. 
c  —  Surface  cracks,  1  inch  section  swelled  to  1  T]2  inches.     Had 

nearly  disintegrated  after  2  days. 
d  —  Surface  cracks. 
e  —  Badly  cracked  on  surface. 
/  —  Badly  cracked  on  surface,  and  1  inch  section  swelled  to 

about  ItV  inches. 

by  additions  of  one  to  three  per  cent.,  but  the  other  brand  is 
practically  ruined  by  the  addition  of  more  than  one  or  two  per 
cent.,  and  both  brands  are  rendered  quite  unsound  by  six 
per  cent,  plaster. 

378.  The  briquets  reported  in  the  preceding  tables  were 
hardened  in  water,  as  usual.  Table  92  gives  some  of  the  results 
obtained  by  adding  plaster  Paris  to  mortars  that  are  hardened 
in  dry  air.  The  effects  on  the  two  samples  of  the  same  brand 
of  Portland,  one  quick  setting  and  one  slow  setting,  are  quite 
different.  The  strength  of  the  quick  setting  sample  is  increased, 
two  per  cent,  giving  the  best  results,  while  that  of  the  slow 


252 


CEMENT  AND  CONCRETE 


setting  sample  is  diminished  by  the  addition  of  plaster.  Both 
brands  of  natural  cement  appear  to  be  notably  improved  by 
the  plaster,  the  best  result  being  given  by  three  per  cent.  Such 
an  addition  to  one  brand  results  in  a  remarkable  increase  in 
strength  of  250  per  cent. 

TABLE   92 

Plaster  of  Paris  in  Cement  Mortars,  Hardening  in  Dry  Air.     Effect 
on  Different  Samples,  Portland  and  Natural 


TENSILE  STRENGTH  POUNDS  PER 

CEMENT. 

| 

SQUARE  INCH,  WITH 
PER  CENT.  OF  CEMENT  REPLACED  BY 

REF. 

|| 

PLASTER  OF  PARIS. 

Kind. 

Brand. 

Sample. 

& 

0 

l 

2 

3 

6 

1 

Port. 

R 

26  R 

6  mo. 

443 

443 

560 

529 

493 

2 

it 

R 

23  R 

u 

559 

483 

419 

436 

337 

3 

Nat. 

An 

L 

(( 

162 

220 

282 

286 

272 

4 

" 

In 

28  S 

u 

76 

110 

151 

269 

240 

NOTES.  —  Sample  26  R,  Portland,  quick  setting,  bears  ^  inch  wire  in  18 

minutes. 
Sample  23  R,  Portland,  slow  setting,  bears  ^  inch  wire  in  244 

minutes. 

Sand,  two  parts  Point  aux  Pins  (river  sand)  to  one  cement. 
All  briquets  stored  in  air  of  laboratory  until  broken. 
Each  result,  mean  of  five  briquets. 

For  the  effect  of  plaster  of  Paris  on  the  adhesive  strength  of 
mortar,  see  §  407. 

379.  Conclusions.  —  It  is  evident  from  the  above  tests  that 
the  addition  of  small  amounts  of  plaster  Paris  affects  different 
samples  of  cement  in  quite  different  ways,  and  it  is  necessary 
to  bear  this  in  mind  in  the  application  of  general  conclusions 
to  special  cases.  The  indications  are  that  the  addition  to 
cement  of  from  one  to  three  per  cent,  of  plaster  of  Paris  or 
sulphate  of  lime  generally  hastens  the  hardening  and  will  not 
usually  result  in  decreased  strength;  that  some  natural  cements, 
however,  are  sensibly  injured  by  more  than  one  per  cent., 
especially  if  used  neat.  The  presence  of  as  much  as  six  per 
cent,  plaster  of  Paris  retards  the  hardening  (although  hastening 
the  initial  set)  and  is  quite  apt  to  ruin  either  Portland  or  natural 
cements.  The  addition  of  plaster  Paris  usually  gives  better 
results  in  air  hardened  than  in  water  hardened  specimens. 


CLAY  WITH  CEMENT  253 

ART.  49.     MIXTURES  OF  CLAY   AND   OTHER   MATERIALS   WITH 

CEMENT 

380.  EFFECT  OF  CLAY  ON  CEMENT  MORTAR  AND  CONCRETE. 

—  Clay  may  occur  in  cement  mortar  or  concrete  due  to  the 
use  of  sand  or  aggregate  that  is  not  clean.  As  the  plasticity  of 
cement  mortar  is  increased  by  the  presence  of  clay,  small 
amounts  are  sometimes  added  to  produce  this  effect,  and  clay 
is  also  sometimes  used  to  render  mortar  stiff  enough  to  with- 
stand immediate  immersion  in  water.  In  the  case  of  concrete, 
the  presence  of  a  certain  percentage  of  clay  renders  it  easier  to 
compact  the  mass  by  tamping,  though  if  too  much  clay  is  pres- 
ent, the  mass  becomes  sticky. 

A  number  of  tests  have  been  made  to  determine  the  behavior 
of  such  mixtures  of  clay  and  cement.  In  all  of  these  tests  the 
clay  was  first  dried,  pulverized  and  sifted,  and  then  a  weighed 
quantity  equal  to  a  given  per  cent,  of  the  weight  of  the  cement 
was  added  to  the  latter.  In  the  writer's  first  tests  of  this  kind 
small  percentages  of  clay  were  used,  less  than  ten  per  cent.,  but 
it  was  found  that  with  lean  mortars  much  larger  percentages  must 
be  used  to  determine  the  point  where  clay  began  to  be  injurious. 

381.  Table  93  shows  the  effect  of  clay  on  the  time  of  setting 
and  soundness  of  neat  cement.     The  effect  of  small  percentages 
of  clay  on  the  time  of  setting  of  Portland  cement  is  not  very 
marked,  but  with  natural  cement  even  ten  per  cent,   of  clay 
retards  the  setting  in  a  marked  degree.     As  to  the  effect  on 
soundness,  Portland  cement  pats  disintegrate  with  more  than 
twenty-five  per  cent,  of  clay  added,  while  the  natural  cement 
is  affected  if  more  than  ten  per  cent,  of  clay  is  present. 

382.  Table  94  shows   the    tensile  strength  of   neat   cement 
mortars  to  which  clay  to  the  amount  of  10  to  100  per  cent,  of 
the  cement  has  been  added.     Some  of  the  Portland  briquets 
were  immersed  as  soon  as  molded,  while  others  were  left  the 
customary  twenty-four  hours  in  moist  air  before  immersion. 

It  is  seen  that  to  mix  clay  with  neat  Portland  cement  results 
in  a  decided  decrease  in  strength,  the  results  obtained  with 
twenty-five  per  cent,  clay  being  only  about  sixty  or  seventy 
per  cent,  of  the  strength  of  the  mortar  without  clay.  With 
natural  cement  the  presence  of  clay  seriously  retards  the  hard- 
ening and  results  in  decreased  strength,  though  it  does  not 


254 


CEMENT  AND  CONCRETE 


TABLE   93 

Effect  of  Pulverized  Clay  on  the  Time  of  Setting  and  Soundness 

of   Cement 


TIME  TO  BEAR  j^  INCH  WIRE  IN  MINUTES, 

AND  THE  CONDITION 

o 

CEMENT. 

CLAY. 

OF  PATS  AFTER  FIVE  MONTHS. 

g 

Clay  as  Per  Cent,  of  Cement. 

w 

Kind. 

Brand. 

Sam- 
ple. 

Kind. 

0 

10 

25 

50 

100 

1 

Portland 

X 

41S 

Red 

285 

318 

328 

328 

450 

1 

u 

I 

' 

t  ; 

Good 

Fair 

Good 

Bad  a 

Bad  a 

2 

i  I 

c 

» 

Blue 

288 

286 

300 

305 

306 

2 

t  c 

' 

c 

" 

Good 

Fair 

Good 

Bad 

Bad  a 

3 

Natural 

Gn 

KK 

Red 

69 

123 

195 

345 

445 

3 

" 

' 

i 

" 

Fair 

Fair 

Bad 

Bad 

Bad  a 

4 

" 

« 

t 

Blue 

98 

173 

215 

350 

415 

4 

" 

i 

c 

H 

Poor  - 

Poor 

Bad 

Bad 

Bad  a 

NOTE.  —  Results  marked  a,  pats  cracked  badly  in  air  and  were  not  im- 
mersed. 

TABLE   94 

Effect  of  Clay  on  Tensile  Strength;   Neat  Cement  Paste 


£  *» 

TENSILE  STRENGTH,  LBS.  PER 

gll 

e 

SQUARE  INCH. 

REF. 

CEMENT. 

KIND 

OF 

CLAY. 

Sig 

H  H 

Clay  Expressed  as  Per  Cent,  of 
Cement. 

*  ^  (B 

pq 

Kind. 

Brand. 

Sample. 

|p 

0 

10 

25 

50 

100 

1 

Port. 

X 

41S 

Red 

24 

3  mo. 

658 

535 

474 

336 

253 

2 

" 

'« 

u 

t  c 

0 

" 

660 

.587 

476 

318 

255 

3 

Nat. 

An 

D 

" 

24 

28  da. 

389 

280 

138 

60 

22 

4 

" 

An 

1) 

" 

24 

3  mo. 

376 

365 

323 

219 

176 

have  as  deleterious  an  effect  as  it  does  with  Portland.  The  mix- 
ing of  clay  with  neat  cement  is  of  course  very  severe  treatment. 

In  Table  95  the  mortars  contain  equal  parts  cement  and  sand, 
and  the  clay  is  from  50  per  cent,  to  200  per  cent,  of  the  weight 
of  cement.  It  appears  from  this  table  that  clay  in  as  large 
amounts  as  50  per  cent,  of  the  cement  is  injurious  to  one-to- 
one  mortars  of  either  Portland  or  natural  cement. 

383.  The  mortars  in  Table  96  are  all  of  Portland,  and  con- 
tain three  parts  sand  to  one  cement.  Smaller  percentages  of 


CLAY  WITH  CEMENT 


TABLE  95 

Effect   of   Large    Amounts    of    Clay    in   Mortars    Containing   Equal 
Parts  Cement  and  Sand 


TENSILE  STRENGTH,  LBS. 

H 

CEMENT. 

•  HOURS 

PER  SQUARE  INCH. 

U 
£ 

KIND 

ELAPSED 

i 

;FERE 

OF 

CLAY. 

BETWEEN 

MOLDING 
AND  IM- 

w    w 

&i 

a 

CLAY  EXPRESSED  AS  PER 
CENT.  OF  CEMENT. 

MM 

MERSING. 

PQ 

Kind. 

Brand. 

Sample. 

0 

50 

100 

150 

200 

1 

Port. 

X 

41  S 

Ked 

24 

3£  mos. 

747 

512 

337 

239 

193 

2 

t  i 

(4 

u 

0 

41 

720 

549 

321 

242 

189 

3 

Nat. 

Gn 

KK 

24 

3  mos. 

454 

241 

212 

183 

140 

4 

u 

(i 

" 

0 

" 

413 

231 

206 

157 

128 

5 

u 

An 

1) 

24 

" 

442 

259 

194 

167 

152 

(i 

u 

u 

u 

0 

" 

440 

274 

184 

141 

125 

7 

ti 

" 

u 

24 

6  mos. 

488 

335 

268 

217 

184 

clay  are  used,  namely,  10  to  40  per  cent.  The  mortars  harden- 
ing in  water  show  a  decided  improvement  due  to  the  presence 
of  clay,  but  the  briquets  hardening  in  the  open  air  indicate  that 

TABLE  96 

Effect  of  Clay  in  Portland  Cement  Mortar  Containing  Three  Parts 
Sand  to  One  Cement 


REFERENCE. 

BRIQUETS  STORXD. 

AGE  OF 
BRIQUETS. 

TENSILE  STRENGTH,  LBS.  PER  SQUARE 
INCH. 

CLAY  ADDED  AS  PER  CENT.  OF  CEMENT. 

0 

10 

'20 

40 

1 

Tank,  Laboratory 

6  months.' 

385 

435 

489 

533 

2 

it              u 

2  years. 

375 

412 

478 

593 

8 

Open  Air 

6  months. 

381 

403 

394 

418 

4 

4  i                  U 

2  years. 

660 

624 

631 

570 

NOTES.  —  Cement,  Portland,  Brand  R,  Sample  83  T. 

Sand,  three  parts  crushed  quartz  f "  to  one  cement  by  weight. 
Clay,  red  clay  dried,  pulverized,  and  passed  through  No.  100 

sieve. 

Clay  added  to  mortar,  amount  cement  and  sand  remaining 
constant. 


256 


CEMENT  AND  CONCRETE 


at  two  years  the  mortar  without  clay  is  stronger.  It  may  be 
noted  in  passing  that  these  results,  obtained  at  two  years,  with 
one-to-three  mortars  hardened  in  open  air,  are  very  high. 

The  effect  of  clay  on  mortars  containing  four  parts  sand  to 
one  cement  is  shown  in  Table  97.  In  this  case  the  addition  of 
clay  equal  to  the  weight  of  the  cement  almost  invariably  re- 
sults in  increasing  the  strength  of  the  mortar.  Briquets  im- 
mersed as  soon  as  made  were  especially  benefited  by  the  pres- 
ence of  clay,  except  in  one  case,  the  red  clay  did  not  appear  to 
increase  the  ability  of  the  natural  cement  Gn  to  withstand 
early  immersion.  The  red  clay  appears  to  give  better  results 
than  the  blue  with  Portland,  while  the  reverse  is  true  with  at 
least  one  brand  of  natural.  Whether  this  difference  is  a  chemi- 
cal or  physical  one  is  not  known;  the  red  clay  is  a  good  pud- 
dling clay,  while  the  blue  clay  is  not,  but  appears  to  contain 
some  very  fine  sand. 

TABLE  97 

Effect  of  Large   Amounts  of  Clay  in   Cement   Mortars    Containing 
Four  Parts  Sand  to  One  Cement 


TENSILE  STRENGTH,  LBS. 

W 

CEMENT. 

HOURS 

05 

PER  SQUARE  INCH. 

£ 

KIND 

ELAPSED 

E 

W 
K 

OF 

CLAY. 

BETWEEN 

MOLDING 
AND  IM- 

o ^  ^ 

S 

CLAY  AS  PER  CEKT.  OF 

CEMENT. 

rt 

MERSING. 

PQ 

Kind. 

Brand. 

Sample. 

0 

50 

100 

150 

200 

1 

Port. 

X 

41  S 

Red 

24 

3  mos. 

271 

348 

305 

239 

193 

2 

Blue 

24 

227 

304 

250 

179 

145 

3 

Red 

00 

156a 

320 

324 

200 

192 

4 

Blue 

00 

149a 

270 

215 

148 

114 

5 

Nat. 

Gn 

KK 

Red 

24 

3  mos. 

138 

155 

146 

164 

133 

6 

Blue 

24 

118 

167 

200 

167 

134 

7 

Red 

00 

83 

87 

39 

86 

72 

8 

Blue 

00 

49 

127 

147 

136 

106 

9 

Red 

24 

2>rs. 

194 

348 

306 

256 

190 

10 

An 

D 

Red 

24 

3  mos. 

138 

218 

174 

174 

190 

NOTES. — Sand,    crushed  quartz   f§,    ("Standard"),   four  parts  to   one 

cement  by  weight. 

Clay,  dried,  pulverized  and  passed  through  sieve  before  using. 
All  briquets  immersed  in  tank  in  laboratory  as  usual. 
Each  result,  mean  of  five  briquets. 
Results  marked  "a,"  briquets  disintegrated  some  on  face  from 

early  immersion. 


CLAY   WITH  CEMENT 


257 


384.  Table  98  gives  the  results  of  tests  by  other  experimenters, 
showing  the  effect  of  clay  on  one-to-three  mortars  of  Portland 
and  natural  cement.1  The  amount  of  clay  used  in  these  tests 
appears  to  be  stated  as  percentage  of  the  total  ingredients  in- 
stead of  as  a  percentage  of  the  cement  as  in  the  preceding 
tables.  The  mortars  were  mixed  quite  dry  for  these  experi- 
ments. The  Portland  cement  mortar  seems  to  be  improved  by 
the  addition  of  clay  to  the  amount  of  twelve  per  cent,  of  the 
mortar.  The  hardening  of  natural  cement  mortar  is  some- 
what slower  with  twelve  per  cent,  clay  than  with  three  to  six 
per  cent.,  but  at  the  age  of  twelve  weeks  the  mortars  containing 
clay  were  all  stronger  than  that  without  clay. 

TABLE  98 
Effect  of  Clay  on  the  Tensile  Strength  of  One-to-Three  Mortars 


TENSILE  STRENGTH,  POUNDS 

CEMENT. 

PARTS 
SAND  TO 

AOE  OF 

BRIQUETS 

PER  SQUARE  INCH.    CLAY  EXPRESSED  AS 
PER  CENT.  OF  MORTAR. 

CEMENT. 

BROKEN. 

0 

3 

6 

9 

12 

Portland 

8 

2  weeks 

202 

267 

280 

318 

333 

tl 

3 

4  weeks 

862 

301 

334 

381 

353 

(( 

3 

12  weeks 

451 

506 

521 

522 

5*7 

Natural 

2 

1  week 

68 

117 

101 

99 

65 

tt 

2 

4  weeks 

152 

199 

219 

170 

146 

*' 

2 

12  weeks 

170 

214 

252 

230 

211 

NOTE.  — Tests  by  Messrs.  J.  J.  Richey  and  B.  H.  Prater. 

385.  Conclusions.  —  Always  keeping  in  mind  the  limitations 
to  be  observed  in  drawing  general  conclusions  from  experi- 
ments having  a  limited  range,  it  may  be  said  that  the  indications 
are  as  follows:  Neat  cement  and  rich  mortars  are  injured  by  the 
addition  of  clay,  the  rate  of  hardening  and  the  ultimate  strength 
being  diminished.  Lean  mortars  containing  three  to  four  parts 
sand  to  one  cement  are  usually  improved  by  the  addition  of 
clay  to  the  amount  of  40  to  100  per  cent,  of  the  cement,  or 
10  to  25  per  cent,  of  the  combined  weight  of  cement  and  sand, 
and  the  ability  of  such  mortars  to  withstand  early  immersion 
may  be  greatly  enhanced  by  such  additions.  It  is  evident 
from  the  above  tests  that  the  expense  which  should  be  incurred 
in  washing  sand  to  remove  a  small  percentage  of  clay  is  limited, 


1  Messrs.  J.  J.  Richey  and  B.  H.  Prater,  Technograph,  1902-3. 


258 


CEMENT  AND  CONCRETE 


and  for  certain  uses  there  is  no  question  that  mortar  may  be 
improved  by  the  addition  of  clay. 

(For  the  effect  of  clay  on  the  compressive  strength  of  con- 
crete, see  Art.  55.) 

386.  Powdered  Limestone,  Brick,  etc.  —  Various  foreign  sub- 
stances are  sometimes  used  with  cement,  either  in  lieu  of  sand, 
or  to  make  the  mortar  more  plastic.  Such  foreign  ingredients 
may  also  occur  in  mortar  as  impurities  in  the  sand  used.  Pow- 
dered limestone,  slaked  lime,  powdered  brick  and  clay  are  some 
of  the  materials  experimented  with  in  this  connection.  A  few 
tests  of  the  effects  of  such  mixtures  on  the  setting  time  of  ce- 

TABLE   99 

Foreign  Substances  in  Cement  Mortar 


CEMENT. 

*% 

TENSILE  STRENGTH,  POUNDS  PER 
SQUARE  INCH. 

w 

0 

&% 

AGE  OF 

fe 

u 
« 

*>«« 

£  fc  s 

BRIQUETS 
WHEN 

Composition  of  Mortar. 

a 
K 

H 

Kind. 

Brand. 

Sam- 
pie. 

«0» 

BROKEN. 

tf 

fcg 

a 

b 

c 

d 

e 

/ 

1 

Port. 

R 

JJ 

None 

8  months 

705 

674 

583 

615 

667 

2 

' 

3.75 

5  days,  H 

152 

217 

164 

175 

240 

198 

3 

' 

3.75 

3  months 

259 

367 

297 

284 

311 

304 

4 

' 

3.75 

1  year 

309 

365 

367 

333 

438 

438 

5 

Nat. 

An 

G 

None 

3  months 

286 

203 

307 

154 

203 

6 

i 

4 

5  days,  h 

86 

.  .  . 

105 

94 

132 

164 

7 

t 

4 

3  months 

185 

214 

157 

239 

215 

8 

i 

4 

1  year 

210 

:.  . 

234 

238 

263 

264 

NOTES.  — Sand,  "Standard."  Materials  added  to  mortar  were  first  pul- 
verized and  passed  through  No.  80  sieve,  holes  .007  inch 
square. 

(  5-day  results,  H  =  immersed  in  hot  water,  80°  C. 
I  5-day  results,   h  =  immersed  in  hot  water,  60°  C. 
Composition  of  mortars:  — 

a  —  No  foreign  substance. 

b  —  No  foreign  substance,  but  additional  amount  cement  added, 

making  mortar  1  to  3  instead  of  Ito  3.75. 

c  — •  Kelleys  Isd.  Limestone,  equal  to  25  per  cent,  weight  of  ce- 
ment added  to  mortar. 
d  —  Slaked  lime  powder,  equal  to  25  per  cent,  weight  of  cement 

added  to  mortar. 
e  —  Red  clay,  equal  to  25  per  cent,  weight  of  cement  added  to 

mortar. 

/  —  Red  brick,  equal  to  25  per  cent,  weight  of  cement  added 
to  mortar. 


FOREIGN  SUBSTANCES   WITH  CEMENT 


259 


ment  indicated  that  the  rate  of  setting  of  Portland  cement  was 
not  appreciably  affected  by  the  addition  of  twenty-five  per 
cent,  of  any  of  these  substances,  but  the  setting  time  of  natural 
cement  appeared  to  be  sensibly  hastened  by  such  additions. 
None  of  these  materials  had  any  appreciable  effect  on  the 
soundness  of  either  Portland  or  natural. 

Table  99  shows  the  effect  on  the  tensile  strength  of  mortar 
of  adding  twenty-five  per  cent,  of  each  of  the  four  substances 
mentioned.  It  appears  that  the  strength  of  neat  cement  mor- 
tar, either  Portland  or  natural,  is  usually  diminished  by  the 
presence  of  such  materials,  but  in  almost  every  case  mortars 
containing  about  four  parts  sand  to  one  cement  are  improved 
by  the  addition  of  the  substances  in  question  to  an  amount 
equal  to  twenty-five  per  cent,  of  the  cement.  Pulverized  clay 
and  brick  give  the  best  results,  the  increased  strength  amounting 
to  from  twenty  to  forty  per  cent. 

387.  Sawdust.  —  Where  a  very  light  and  porous  mortar  is 
desired  for  use  in  floors  and  similar  purposes,  the  incorporation 
of  sawdust  in  the  mortar  is  suggested  by  a  similar  use  in  clay 
building  materials.  The  results  in  Table  100  show  that  the 
use  of  sufficient  sawdust  to  materially  diminish  the  weight 
practically  ruins  the  cohesion  of  the  mortar,  even  ten  per  cent, 
of  sawdust  materially  diminishing  the  strength. 

TABLE   100 
Sawdust  in   Cement  Mortar 


REFERENCE. 

CEMENT. 

PARTS  SAND  TO 
ONE  CEMENT. 

BRIQUETS 
STORED. 

AGE  OF 
BRIQUETS  WHEN 
BROKEN. 

TKNSILK  STRENGTH  POUNDS  PER 
SQUARE  INCH. 

Kind. 
Port. 

u 
u 
(1 

Nat. 
it 

Brand. 

Sawdust  as  Per  Cent,  of  Cement. 

0 

10 

20 

25 

50 

100 

1 
2 

;) 
4 
5 
6 

X 

(1 
(( 
(1 

An 
it 

0 
0 
2 
2 
0 
2 

Tank 
Dry  air 
Tank 
Dry  air 
Tank 
Tank 

lyr. 

It 
(( 
14 

[( 

11 

799 
074 
502 
452 
433 
313 

409 
492 

169 
103 

44 
28 
32 
14 

38 
58 

31 
a 
32 

a 
b 

20 

253 

129 
108 

104 

NOTES.  —  Sand,  crushed  quartz,  f $.     Sawdust  from  white  pine,   passed 

through  sieve  with  one-quarter  inch  meshes, 
a  —  Briquets  broken  in  applying  initial  strain. 
b  —  Briquets  disintegrated  in  tank. 


260 


CEMENT  AND  CONCRETE 


388.  Use  of  Ground  Terra  Cotta  as  Sand.  —  A  light  weight 
mortar  may  also  be  made  by  using  as  sand  or  aggregate,  ma- 
terials of  burned  clay,  such  as  brick  or  terra  cotta.  The  tests 
in  Table  101  were  made  to  determine  the  value  of  ground  terra 
cotta  for  use  in  place  of  sand,  and  it  appears  that  this  material 
gives  excellent  results.  The  strength  given  with  one  of  the 
brands  of  natural  cement  is  especially  high. 

TABLE   101 
•  Use  of  Ground  Terra  Cotta  as  Sand  in  Cement  Mortar 


a 

TENSILE  STRENGTH,  LBS.  PER  SQ.  IN. 

<J 

w 

AGE  OF 

Parts  Ground  Terra  Cotta  to  One  Cement. 

K 
h 

BRIQUETS. 

by  Weight. 

Kind. 

Brand. 

1 

2 

3 

4 

6 

1 

Portland 

X 

3  months 

523 

406 

332 

257 

174 

2 

u 

" 

1  year 

604 

518 

429 

337 

266 

3 

Natural 

An 

3  months 

284 

338 

346 

347 

224 

4 

'• 

(C 

1  year 

262 

360 

351 

361 

186 

5 

u 

En 

3  months 

291 

303 

184 

136 

6 

u 

1  1 

1  year 

340 

434 

284 

161 

NOTES.  —  Terra  Cotta  tile,  of  medium  burn,  ground  and  passed  through 
No.  20  sieve,  and  used  in  place  of  sand. 

ART.  50.     THE  USE  OF  CEMENT  MORTARS  IN  FREEZING 
WEATHER 

389.  It  is  frequently  desirable  to  use  cement  in  freezing 
weather,  but  to  ensure  good  work  under  these  circumstances  it 
is  necessary  to  take  certain  precautions.  If  mortar  is  frozen 
immediately  after  mixing,  setting  cannot  take  place  until  it 
has  again  thawed.  In  the  practical  use  of  cement  it  is  always 
gaged  with  a  larger  quantity  of  water  than  is  required  for  the 
chemical  combination,  and  if  this  excess  water  is  frozen  after 
the  setting  is  somewhat  progressed,  the  consequent  expansion 
may  be  sufficient  to  disrupt  the  partially  set  mortar.  By  warm- 
ing the  materials  or  by  lowering  the  freezing  point  of  the  water 
by  the  addition  of  salt,  glycerine,  or  some  other  substance  hav- 
ing this  effect,  it  is  sought  to  prevent  the  mortar  freezing  until 
the  work  is  protected  by  another  layer  of  mortar,  or  otherwise, 
and  thus  to  avoid  the  expansion.  Salt  is  generally  used  much 


EXPOSURE   TO  FROST  261 

too  sparingly  to  prevent  freezing.  The  freezing  point  of  water 
is  lowered  about  one  and  a  half  degrees  Fahr.  for  each  per  cent, 
of  common  salt  added;  thus  a  twenty  per  cent,  solution  would 
freeze  at  about  two  degrees  Fahr. 

390.  The  following  tests  are  selected  as  showing  typical  re- 
sults of  a  large  number  of  experiments  made  under  the  author's 
direction  to  determine  the  effect  of  exposing  cement  mortars  to 
frost,  and  to  indicate  what  treatment  will  alleviate  the  delete- 
rious effects  of  low  temperature.     In  making  tests  with  small 
specimens,  it  is  difficult  to  approach  the  conditions  existing  in 
the  actual  use  of  mortars  in  freezing  weather.     A  small  mass 
of  mortar  exposed  to  the  air  on  all  sides  sets  more  quickly  than 
the  interior  of  a  large  mass;  and  on  the  other  hand,  the  effect 
of  frost  on  a  small  specimen  must  be  more  severe  and  more 
quickly  apparent.     Many  of  the  results  are  more  or  less  contra- 
dictory, and  the  conclusions  that  have  been  drawn  are  such  as 
appear   to   be   indicated   by   the   majority   of   the   tests.     The 
treatment  of  the  briquets,  and  the  conditions  existing,  are  given 
in  some  detail,  that  the  limits  of  applicability  of  such  conclu- 
sions may  be  seen. 

391.  Exposure   to  Frost   of   Mortars  Already  Set.  —  In   the 
tests  recorded  in  Tables  102  to  104  the  briquets  were  allowed  to 
remain  one  or  two  days  in  the  laboratory.     It  is  evident  that 
these  results  are  of  but  limited  practical  importance,  since  it 
is  seldom  that  mortars  which  are  made  in  winter  can  be  allowed 
to  set  in  a  warm  place  before  exposure;  they  are  given,  how- 
ever, for  what  they  are  worth.     Tables  102  and  103  give  the 
results  obtained  with  Portland  cement  briquets  exposed  to  a 
severe  temperature  twenty-four  to  forty-eight  hours  after  made. 
The  most  important  deduction,  and  the  one  most  clearly  indi- 
cated by  these  tables,  is  that  Portland  cement  mortar  made  with 
fresh  water  may  be  subjected  to  very  low  temperatures  twenty- 
four  to  forty-eight  hours  after   molded,   without  seriously  de- 
creasing the  tensile  strength  given  at  six  months  to  two  years. 
It  also  appears  that  solutions   containing  as   much  as   fifteen 
per  cent,  salt  are  deleterious,  and  smaller  percentages  are  not 
advantageous  under  these  conditions. 

Table  104,  giving  the  results  of  similar  tests  with  natural 
cement  mortar,  indicates  that  this  brand  gives  good  results  if 
allowed  to  set  in  warm  air  before  exposure  to  frost.  Solutions 


262 


CEMENT  AND  CONCRETE 


TABLE   102 

Exposure  of  Portland  Cement  Mortars  to  Low  Temperatures  after 
Twenty-four  Hours  in  Laboratory 


AGE 

TENSILE  STRENGTH,  POUNDS  PER  SQ.  IN. 

SAND,   KIND. 

DATE 

WHEN 

MADE. 

BROKEN. 

a 

b 

c 

d 

e 

/ 

g 

Standard  .    .    . 

1-15 

6  mo. 

772 

960 

816 

524 

507 

Standard  .     .     . 

1-15 

21  mo. 

796 

882 

766 

443 

642 

Pt.  aux  Pins,      ) 

1-18 

6  mo. 

651 

630 

769 

463 

443 

pass,  sieve  f  10  } 

1-18 

21  mo. 

760 

780 

•    • 

711 

543 

447 

NOTES.  —  Cement,  Portland,  Brand  R.     One  part  sand  to  one  cement. 

Briquets  made  in  laboratory,  temp.,  64°  to  66°  Fahr. ;  materials 

about  65°  Fahr. 

Temperature,  open  air,  Jan.  16  to  Jan.  19,  4°   to  15°  Fahr. 
Treatment  of  briquets:  — 

a  —  Fresh  water,  briquets  stored  in  water  in  laboratory. 
b  —  Fresh  water,  briquets  stored  in  open  air  after  24  hours. 
c  —  Fresh  water,  briquets  alternated,  two  days  in  open  air 
and    then   two  days  in  air  laboratory,  for  fifty-two 
days,  then  left  in  open  air. 

d  —  Water  5  per  cent,  salt;  briquets  stored  in  open  air. 
e  —  Water  15  per  cent  salt;  briquets  stored  in  open  air. 
/  —  Water  25  per  cent,  salt;  briquets  stored  in  open  air. 
g  —  Water  25  per  cent,  salt;  briquets  stored  in  water  in  lab. 

TABLE  103 

Exposure  of  Portland  Cement  Mortars  to  Low  Temperatures, 
Twenty-four  to  Forty-eight  Hours  after  Made 


SAND, 
KIND. 

DATE 
BRIQUET 

MADE. 

AGE 
WHEN 
BROKEN. 

TENSILE  STRENGTH,  POUNDS  PER  SQ.  IN. 

a 

6 

c 

d 

e 

/ 

g 

h 

i 

j 

Std.  . 
Std.  . 

p.  p. 
p.  p. 

1-16 
1-16 
1-19 
1-19 

6  mo. 
21  mo. 
6  mo. 

415 

602 

372 
372 

401 
438 

262 

384 

202 
326 

381 
638 

394 
430 

360 
418 

371 
375 

233 
344 

21  mo. 

NOTES.  —  Cement,  Portland,  Brand  R.    Three  parts  sand  to  one  cement. 

Briquets  made  in  laboratory.  Temp . :  Air  and  materials,  64°  to 
67°  Fahr.  Open  air,  Jan.  10  to  20, -15°  to  +18°  Fahr. 

Treatment  of  briquets:  a,  b,  c,  d  and  e  mixed  with  water  con- 
taining 0,  10,  15,  20  and  25  per  cent,  salt,  respectively; 
a  to  d,  inclusive,  air  laboratory  24  hours,  water  laboratory 
16  hours,  air  laboratory  12  hours,  then  in  open  air. 

/,  g,  h,  i  and  /,  mixed  with  water  containing  0,  10,  15,  20  and 
25  per  cent,  salt,  respectively. 

e  to  /,  inclusive,  put  in  open  air  after  about  24  hours  in 
air  of  laboratory. 


EXPOSURE   TO  FROST 


263 


TABLE  104 

Exposure  of  Natural  Cement  Mortars  to  Low  Temperatures, 
Twenty-four  Hours  after  Made 


PARTS 

SAND  TO 
ONE 

DATE  MADE. 

AGE  WHEN 
BROKEN. 

TEN 

SILE  STRENGTH,  POUNDS  PER  SQ.  IN. 

CEMENT. 

a 

6   |   c 

d 

e 

/ 

2 

1-20 

H  ino. 

297 

404 

319 

297 

170 

2 

1-20 

lyr. 

305 

390 

343 

273 

217 

4 

1-20 

6  mo. 

222 

318 

319 

344 

114 

4 

1-20 

lyr. 

223 

259 

339 

205 

.  .  . 

150 

NOTES. — Cement,  Natural,  Brand  On.  Sand,  "  Pt.  aux.  Pins"  (river 
sand). 

Temp,  materials  and  air  of  laboratory  where  briquets  were 
molded,  65°  to  68°  Fahr.  Temp,  open  air  Jan.  21  to  23, 
-  1°  to  +  29°. 

Treatment  of  briquets:  a,  briquets  stored  in  water  in  labora- 
tory, b  to  /,  inclusive,  briquets  stored  in  open  air  after 
twenty-four  hours  in  air  of  laboratory. 

a  and  b,  fresh  water  used  for  gaging  mortar. 

c,  d,  e  and  /,  water  used  in  gaging  had  5,  10,  15  and  25  per 
cent,  salt,  respectively. 

containing  more  than  ten  per  cent,  salt  are  deleterious  for  such 
treatment.  Briquets  of  another  brand  of  natural  cement,  a 
one-to-one  mortar  of  which  gave  about  450  pounds  tensile 
strength  at  one  year,  failed  entirely  when  placed,  one  hour 
after  made,  in  open  air  for  three  days,  and  then  immersed  in  a 
tank  in  the  laboratory.  A  7.4  per  cent,  solution  of  salt  used 
for  gaging  assisted  very  materially  in  preserving  the  mortar 
under  the  same  severe  treatment,  although  this  amount  of  salt 
was  not  sufficient  to  lower  the  freezing  point  of  the  water  below 
the  temperature  to  which  the  briquets  were  subjected. 

392.  Effect  of  Salt  in  Mortars  Hardened  in  Water  and  Air.  - 
In  the  tests  recorded  in  Table  105  the  materials  used  were  at  "a 
temperature  of  forty  degrees  Fahr.,  and  the  briquets  were 
molded  in  an  open  warehouse  where  the  temperature  was  usually 
below  twenty-three  degrees  Fahr.,  though  for  a  few  of  the 
tests  the  temperature  of  the  air  at  time  of  molding  was  as  high 
as  twenty-seven  degrees.  The  temperature  of  the  mortar 
when  briquets  were  finished  was  usually  but  little  above  thirty- 
two  degrees  Fahr.  The  briquets  were  left  in  a  warehouse  for 
three  days,  when  part  of  them  were  immersed  in  cold  water 


2G4 


CEMENT  AND  CONCRETE 


Water  Used 
g. 


er  Cent.  Salt 
G 


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EXPOSURE   TO  FROST 


265 


(under  ice),  and  the  remainder  stored  in  open  air  on  a  shelf 
covered  by  a  rough  board  roof,  but  with  front  left  open  to  the 
weather.  All  mortars  contained  two  parts  river  sand  to  one  of 
cement  by  weight.  The  water  used  in  gaging  varied  from 
Iresh  to  a  twenty-five  per  cent,  solution. 

The  results  indicate  that  Portland  mortars  made  in  low 
temperatures,  to  be  immersed  in  cold  water,  are  improved  by 
fifteen  to  twenty  per  cent,  salt  in  the  water  of  gaging,  but  that 
more  than  five  per  cent,  salt  is  deleterious  for  mortars  exposed 
to  the  air  only.  The  very  high  results  given  by  the  air-hardened 
specimens  are  worthy  of  notice. 

A  similar  series  of  tests  of  natural  cement  gave  results  from 
which  no  definite  general  conclusions  could  be  drawn.  The 
effect  of  freezing  and  of  the  use  of  salt  varied  greatly  for  dif- 
ferent samples.  For  any  given  sample  the  treatment,  as  re- 
gards the  use  of  salt,  giving  good  results  in  open  air,  was  usually 
the  reverse  of  that  giving  good  results  in  cold  water.  The 
conclusions  indicated  for  rich  mortars  were  sometimes  the  re- 
verse of  those  shown  by  lean  mortars. 

393.    The  results  obtained  with  five  brands  of   natural  ce- 

TABLE   106 
Effect   of  Low  Temperatures   on   Five  Brands    of   Natural  Cement 


M                * 

g 

a' 

K       U 

H 

O 

w 

Q 

BJ 

g 

1  | 

03  « 

U 

w 

U       "if. 

MEAN  TENSILE  STRENGTH, 

H 
U 

U 
H 

K 

£ 

03 

E 

<* 

Ps 

Jl 

U 

g 

2&I 

BRAND. 

tf 

q 

PH 

u     sc 
H    £ 

K  M 
U 

1 

S    1 

Gn. 

An. 

Kn. 

Hn. 

Jn. 

a 

& 

c 

rf 

e 

/ 

g 

h 

i 

J 

k 

• 

Mo.  Da. 

Deg. 

Days 

1 

2     20 

N 

1 

9-11 

18 

Canal 

234 

322 

285 

423 

284 

2 

2     22 

N 

1 

16-19 

0 

u 

. 

201 

327 

326 

302 

211) 

3 

2     20 

S 

1 

9-11 

18 

Open  air 

o' 

344 

416 

412 

321 

292 

4 

2     22 

S 

1 

16-19 

0 

" 

0 

367 

305 

480 

360 

311 

5 

2     20 

S 

1 

9-11 

18 

ti 

7 

274 

306 

413 

244 

304 

6 

2     22 

S 

1 

16-19 

0 

u 

7 

292 

338 

426 

311 

304 

7 

2     21 

N 

2 

7-14 

19 

Canal 

. 

161 

318 

329 

348 

238 

8 

2     23 

N 

2 

9-9 

0 

it 

160 

217 

355 

2-38 

186 

9 

2     21 

S 

2 

9-14 

19 

Open  air 

'o 

288 

289 

382 

282 

319 

10 

2     23 

S 

2 

9-9 

0 

" 

0 

338 

275 

422 

423 

367 

11 

2     21 

S 

2 

9-14 

19 

u 

3 

268 

271 

340 

240 

295 

12 

2     23 

S 

2 

9-9 

0 

l( 

7 

317 

333 

414 

345 

356 

NOTE. — All  briquets  broken  when  six  and  a  half  months  old. 


266 


CEMENT  AND  CONCRETE 


ment  are  given  in  Table  106.  The  briquets  were  made  in  a 
temperature  of  nine  to  nineteen  degrees  Fahr.  Half  of  the 
briquets  were  made  with  fresh  water,  and  half  with  water  con- 
taining enough  salt  to  lower  its  freezing  point  below  that  of  the 

TABLE   107 

Portland  Cement  Mortar  in  Low  Temperatures 
Effect  of  Heating  Materials 


H 
o 

!fi 

H  PS 
«  K  « 
D  <  ^    • 
&(£  W  Q 

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Pi 
Qp 

QUETS 
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TENSILE  STRENGTH,  POUNDS 
PER  SQUARE  INCH. 

55 

s 

P5 
K 

P 

Sfe  a  3 

g§£3 

S  w  M  o 

WHERE 
STORED. 

& 

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P3« 
ft,  Z 

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Ma- 

Warm 
Ma- 

Cold 
Ma- 

Warm 
Ma- 

H 

H  H 

P*     £ 

g  PS  5§ 

«  O^j1^ 

^    £ 

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o  a 

terials, 

terials, 

terials, 

terials, 

ri 

£° 

fH«^ 

1       Q 

W 

OH 

PQ 

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110°. 

40°. 

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Mo. 

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23 

Canal 

Wet 

6 

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582 

598 

2 

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590 

593 

3 

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737 

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542 

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14 

i 

181 

549 

597 

8 

2 

23-24 

0 

t 

« 

467' 

541 

Means 

£70 

587 

596 

620 

9 

1 

4-6 

23 

Open  air 

Dry 

6i 

469 

450 

10 

1 

9-10 

0 

" 

711 

724' 

11 

1 

4-6 

23 

Wet 

487 

470 

12 

1 

9-10 

0 

(t 

628' 

614 

13 

2 

15-18 

14 

Dry 

507 

'542' 

14 

2 

24-25 

0 

u 

673 

657 

15 

2 

15-18 

14 

Wet 

422 

453 

16 

2 

24-25 

0 

" 

543 

495 

Means 

639 

622 

471 

479 

Grand 

Means 

605 

605 

534 

549 

NOTES. —  Cement,  Portland.     Sand,  "  Point  aux  Pins." 

When  warm  materials  used,  the  temperature  mortar  after  briquets 
finished,  63°  to  71°  Fahr. 

When  cold  materials  used,  the  temperature  mortar  after  briquets 
finished,  32°  to  39°  Fahr. 

When  salt  water  used  for  mixing,  water  was  23  per  cent,  salt  for 
1  to  1  mortars  and  14  per  cent,  salt  for  1  to  2  mortars. 

Briquets  stored  in  canal  were  left  in  cold  air  three  days  before 
immersion. 

Part  of  briquets  stored  in  open  air  were  immersed  in  tank  in  labo- 
ratory one  week  just  before  breaking,  while  others  were  broken 
dry  as  indicated. 

In  general,  each  result  is  mean  of  five  briquets. 


EXPOSURE   TO  FROST 


267 


air  where  the  briquets  were  made.  The  results  are  chiefly  of 
interest  as  showing  the  strength  that  may  be  attained  by  natural 
cement  mortars  under  these  severe  conditions. 

Higher  results  are  usually  given  by  the  air-hardened  speci- 
mens than  by  those  immersed  in  cold  water,  though  this  de- 
pends somewhat  upon  the  brand.  Salt  is  usually  beneficial  if 
the  briquets  are  immersed,  and  detrimental  for  open  air  ex- 
posure. 

394.  Effect  of  Heating  the  Materials.  —  The  tests  in  Table 
107  were  made  to  determine  the  effect  of  heating  the  materials 
when  working  in  low  temperatures,  and  thus  delaying  for  a 
time  the  freezing  of  the  mortars.  The  details  of  the  tests  are 
fully  given  in  the  table.  The  conclusion  indicated  is  that  the 
ingredients  may  be  used  cold  or  warm  indifferently.  A  gain  of 
only  four  per  cent,  is  indicated  for  warm  materials  in  mortars 
mixed  with  salt  water  and  hardened  in  cold  fresh  water.  In 
practical  work,  however,  the  use  of  warm  materials  may  so  delay 
the  freezing  as  to  permit  thorough  tamping  before  the  mortar 
freezes.  Table  108  gives  similar  results  with  one  brand  of  natural 
cement,  from  which  it  appears  that  warm  materials  have  a  slight 
advantage  for  either  cold  water  or  cold  air  hardening. 

TABLE   108 

Natural  Cement  Mortars  in  Freezing  Weather 
Effect  of  Heating  Materials 


2^ 

£* 

TENSILE  STRENGTH,  POUNDS  PER  SQ.  IN. 

a 

a* 

Is 

fc 
H 
H 

Sa 

QQB 

TURE  AlR 

WHERE 

~o 

fflS 

STORED  IN  CANAL. 

STORED  IN  OPEN  AIR. 

00° 

BRIQUETS 

fc  Z 

3 

H  H 

MOLDED 

o* 

£ 

S| 

B»W 

Materials. 

Materials. 

Materials. 

Materials. 

ftn^ 

$* 

32°  F. 

100°  F. 

32°  F. 

100°  F. 

Deg.  Fahr. 

1 

3 

15  to  16 

6  mos. 

140 

151 

311 

372 

2 

3 

15  to  19 

9     " 

175 

203 

.    . 

.    . 

3 

2 

22  to  24 

9     " 

167 

204 

355 

361 

NOTES.  —  Cement,  Brand  Gn,  Natural.     All  mortars  made  with  fresh  water. 
Briquets  made  with  warm  materials  were  frozen  in  from  15  to  24 

minutes  after  made. 
Each  result,  mean  of  ten  briquets. 


268 


CEMENT  AND  CONCRETE 


395.  Consistency  of  Mortars  to  Withstand  Frost.  —  Since  the 
injury  due  to  frost  is  caused  by  the  expansion  of  the  water 
used  in  gaging,  it  would  be  expected  that  mortars  mixed  wet 
would  suffer  most.  This  conclusion  is  confirmed  by  the  tests 
in  Table  109.  The  superiority  of  dry  mortars  is  especially 
shown  in  mortars  that  harden  in  the  air.  The  treatment  to 
which  these  briquets  were  subjected  was  very  severe,  yet  the 
results  are  excellent. 

TABLE   109 

Consistency   of  Mortars   as  Affecting  Ability  to  Withstand   Low 

Temperatures 


AGE  OF 
BKIQUETS 
WHEN 
BROKEN. 

TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

STORED  IN  CANAL. 

STORED  IN  OPEN  AIR. 

a 

b 

c 

d 

e 

/ 

!l 

h 

6  mos. 

414 

414 

372 

501 

601 

571 

521 

674 

0  mos. 

474 

4(58 

431 

527 

727 

022 

525 

563 

NOTES.  — Cement,  Portland,  Brand  R;sand,  "  Point  aux  Pins,"  passing  holes 
.08  inch  sq.     Two  parts  sand  to  one  cement  by  weight.    Each 
"*          result,  mean  of  five  briquets. 
Temperature,  air  where  briquets  were  molded,  13°  to  14°  Fahr.; 

materials  used,  40°  Fahr. 

Temperature  mortar  when  molding  completed  32°  to  36°  Fahr. 
Briquets  made  with  fresh  water  had  frozen  after  30  minutes. 
Treatment  briquets:  — a  to  d,  stored  in  canal  (under  ice). 

e  to  hj  stored  in  open  air,  January,  North- 
ern Michigan. 

Water  used:  —  a  and  e,  10.4  per  cent,  fresh  water. 
b  and  /,  11.9  per  cent,  fresh  water. 
c  and  g,  13.3  per  cent,  fresh  water. 
d  and  h,  11.9  per  cent,  water  containing  15  per 
cent.  salt. 

396.  Fineness  of  Sand  and  Effect  of  Frost.  —  The  briquets 
reported  in  Table  110  were  made  from  mortar  containing  one 
and  two  parts  limestone  screenings  to  one  cement,  the  screen- 
ings varying  from  coarse  to  fine.  In  general,  the  results  follow 
the  rule  applicable  to  mortars  used  in  ordinary  temperatures, 
namely,  that  the  coarse  sands  give  the  best  results;  but  it 
appears  that  the  briquets  made  with  fresh  water  and  exposed 


EXPOSURE   TO  FROST 


260 


o     ^ 


o  75 
.1?  & 

a  a 


wj 

0) 

Q 


s  a  H  w 

2°  OCQ  < 


£     £      2      2 

_z        jr        —        ^: 
OS       .00       .OS      .00 


£  a  S  ?  c  c 
^  ^  S  ^  op  ^ 


2 
p 

£5 


|> 

Jl 


II 


•OKIOVQ 
Nl   aaSQ    H3XV^   NI 

xivg  -XN33  uaj 


•UHVJ  -o 
aavj^  bxa 

3H3HM 

aHaxvaadwaj, 


•xNiawaj 


•XHOiaAi 

AS   XN3W3Q    3NQ   Oi 
80NIN33HOg 

anoxeawi^  sxavj 


o  :  ^  ^  c  »  o2 


GO        ^        O        »-*  -M 

~IJ      """^      rHJ.      ^^      5^1-H 

"  »"*  (M"  co"  o?o 


H  H  >s 

.5       ^  —  c 

O>  0)  O 

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^  2^ 


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S!!! 


270  CEMENT  AND  CONCRETE 

in  open  air  reverse  this  rule,  either  the  finest  sand,  fg,  or  the 
f  g  giving  the  best  result. 

397.  CONCLUSIONS.  —  The  following  conclusions  concerning 
the  use  of  cement  mortars  in  freezing  weather  appear  to  be  indi- 
cated by  the  foregoing  tests: 

1st,  Mortars  should  not  be  mixed  wet  for  use  in  low  tem- 
peratures. 

2d,  Portland  cement  mortars  made  in  cold  weather  usually 
develop  a  good  tensile  strength,  especially  when  exposed  to  the 
open  air. 

3d,  Portland  cement  mortars  for  open  air  exposure  may  be 
benefited  by  the  use  of  from  three  to  seven  per  cent,  salt  in 
the  water  used  in  gaging,  and  from  ten  to  twenty  per  cent, 
salt  in  the  gaging  water  may  prove  beneficial  for  mortars  hard- 
ening in  cold  water. 

4th,  Warming  the  materials  for  Portland  cement  mortar 
appears  to  have  but  little  effect  on  its  frost  resisting  qualities. 

5th,  Coarse  sand  usually  gives  the  best  results  in  Portland 
mortars  made  in  cold  weather,  but  fresh  water  briquets  ex- 
posed in  open  air  appear  to  give  better  results  with  fine  sand. 

6th,  Some  natural  cements  give  fairly  good  results  in  freez- 
ing weather,  while  others  are  practically  destroyed  by  severe 
exposure.  The  effect  of  variations  in  treatment  on  different 
brands  of  natural  cement  is  so  varied  that  no  general  conclu- 
sions can  be  drawn  from  the  above  tests,  but  the  indications 
are  that  salt  water  for  gaging  is  beneficial  if  the  mortar  hardens 
in  cold  water,  but  detrimental  for  mortars  exposed  to  the  open 
air. 

ART.  51.     THE  ADHESION  OF  CEMENTS 

398.  THE  ADHESION  BETWEEN  PORTLAND  AND  NATURAL 
CEMENTS.  —  The  question  sometimes  arises  as  to  whether  Port- 
land cement  will  adhere  to  natural  cement  already  set,  and 
whether  fresh  natural  and   Portland   cement  mortars  may  be 
used  together,  as  in  the  case  of  a  Portland  facing  mortar  used 
with  natural  cement  concrete.     Tests  bearing  on  these  points 
are  given  in  Tables  111,  112  and  113. 

In  the  tests  in  Table  111  fresh  Portland  cement  mortar  was 
applied  to  natural  cement  mortar  that  had  set  seven  days. 
Natural  cement  briquets,  made  neat  and  with  one  to  four 
parts  sand,  as  seen  in  the  headings  of  the  columns  of  the  table, 


ADHESION  PORTLAND  AND  NATURAL 


271 


were  broken  at  the  age  of  seven  days.  The  fresh  Portland 
mortar  was  applied  to  the  half  briquets  on  the  same  day  that 
the  latter  were  broken,  by  placing  the  half  briquet  in  one  end 
of  the  mold,  and  filling  the  other  half  of  the  mold  with  fresh 
Portland  mortar  of  the  composition  shown  in  the  second  column. 

TABLE  111 

The  Adhesion  of  Portland  Cement  to  Hardened  Natural  Cement 

Mortar 


REF. 

PARTS    SAND  TO 
ONE  PART 
PORTLAND 
CKMENT  IN 
FRESH  MORTAR. 

ADHESION  OF  PORTLAND  MORTAR  TO  HALF  BRIQUETS  OF 
HARDENED  NATURAL  CEMENT  CONTAINING  PARTS  SAND. 

0 

1 

2 

3 

4 

1 
2 
3 

0 
1 

2 

246 
185 
63 

2-35 
210 
75 

197 
186 
00 

11)4 
152 
84 

161 
120 
85 

NOTES.  —  Briquets  of  natural  cement,  containing  parts  sand  indicated  at  top 
of  columns,  were  broken  at  seven  days.  The  half  briquets 
were  then  placed  in  one  end  of  briquet  mold  and  the  other 
end  of  mold  was  filled  with  fresh  Portland  mortar. 

Fresh  mortar  made  of  Portland  cement,  Brand  R. 

Sand,  "  Point  aux  Pins,"  passing  No.  10  sieve. 

In  general,  each  result  is  mean  of  ten  bnquets. 

Nearly  all  briquets  broke  at  juncture  of  Portland  and  natural 
mortars. 

It  is  seen  that  the  neat  Portland  gave  the  highest  results  in 
adheskm,  the  one-to-one  mortar  giving  a  comparatively  low  ad- 
hesive strength.  It  is  also  seen  that  the  neat  and  one-to-one- 
mortars  adhered  best  to  the  richer  natural  cement  briquets, 
but  the  one-to-two  Portland  gave  the  greatest  adhesi  ve  strength 
with  the  poorer  natural  cement  mortars.  All  of  the  tests  gave 
very  irregular  results. 

399.  To  make  the  briquets  the  results  of  which  are  recorded 
in  Table  112,  a  plate  was  placed  in  the  center  of  the  mold,  one- 
half  of  the  mold  was  filled  with  fresh  natural  cement  mortar, 
the  plate  was  then  withdrawn  and  the  other  half  of  the  mold 
filled  with  fresh  Portland  mortar.  Briquets  in  line  1  were 
made  with  Portland  cement  alone,  while  those  in  line  2  con- 
tained orfly  natural  cement,  these  briquets  being  made  for  pur- 
poses of  comparison.  The  briquets  containing  both  Portland 


272 


CEMENT  AND  CONCRETE 


and  natural  were  made  neat  and  with  from  one  to  three  parts 
sand.  By  noting  the  number  of  briquets  that  broke  at  the 
juncture  between  Portland  and  natural,  it  was  found  that,  in 
general,  the  adhesion  of  rich  Portland  mortar  to  rich  natural 
cement  mortar  is  greater  than  the  strength  of  the  natural,  but 
that  with  the  poorer  mortars  the  adhesion  is  less  than  the 
strength  of  the  natural. 

TABLE  112 
Adhesion  bet-ween  Fresh  Mortars  of  Portland  and  Natural  Cement 


PARTS  SAND  TO  ONE  OF 

ADHESIVE  OR  COHESIVE  STRENGTH,  POUNDS 

TJ  »,T1 

CEMENT. 

PER  SQUARE  INCH. 

K.EF. 

IN  Po  RTLAND 

MORTAR. 

IN  NATURAL 
MORTAR. 

28  days. 

3  months. 

6  months. 

1  year. 

1 

2 

278 

372 

410 

464 

2 

2 

164 

243 

268 

308 

3 

V  ' 

0 

318 

358 

323 

380 

4 

1 

1 

252 

326 

376 

383 

5 

0 

1 

229 

331 

356 

357 

6 

2 

1 

226 

196 

339 

298 

7 

2 

2 

128 

235 

265 

285 

8 

1 

2 

145 

213 

259 

271 

9 

1 

3 

103 

160 

185 

206 

10 

2 

3 

95 

176 

206 

197 

11 

3 

3 

63 

162 

197 

193 

NOTES.  —  Portland  Cement,  Brand  R. 
Natural  Cement,  Brand  An. 
Sand,  "  Point  aux  Pins,"  passing  No.  10  sieve. 
Both  mortars  mixed  fresh  and  filled  in  opposite  ends  of  mold. 

400.  In  Table    113   the   natural   cement   mortar   contained 
three  parts  sand  to  one  of  cement,  while  the  richness  of  the 
Portland  mortars  varied  from  neat  to  four  parts  sand.     Four 
combinations  of  different  brands  were  used.     Brand  R,  Port- 
land, and  brand  An,  natural,  appear  to  give  the  best   results 
together.     It  is  also  seen  from  this  table  that  the  adhesion  of 
the  rich  Portland  mortar  is  greater  than  the  cohesive  strength 
of  the  natural  cement,  but  when  the  Portland  mortar  contains 
three  or  four  parts  sand   to  one  cement,  the  adhesion  is  less 
than  the  strength  of  the  natural  cement  mortar. 

401.  THE  ADHESION  TO  STONE  AND  OTHER  MATERIALS.  — 
Since  cement  mortars  are  usually  employed  to  bind  <>ther  ma- 
terials together,  it  follows  that  the  adhesive  strength  is  of  the 


ADHESION   TO   VARIOUS  MATERIALS 


273 


greatest  importance.  On  account  of  the  difficulty  of  making 
tests  of  adhesive  strength,  however,  the  data  concerning  it  are 
very  meager.  Two  methods  have  been  employed  by  the  au- 
thor in  making  such  tests.  One  method,  used  for  brick,  is 
to  cement  two  bricks  together  in  a  cruciform  shape.  The  other 
method  consists  in  placing  small  blocks  of  the  substance  to  be 
used  in  the  center  of  a  briquet  mold,  and  filling  the  ends  of 
the  mold  with  the  desired  mortar. 

TABLE   113 
Adhesion  between  Fresh  Mortars  of  Portland  and  Natural  Cement 


p 
a 

CEMENT 

\R. 
EMENT. 

NATURAL  CEMENT 
MORTAR. 

QUET8. 

ADHESIVE  STRENGTH  POUNDS  PER 
SQUARE  INCH. 

a  HO 

M 

Parts  Sand  to  One  Cement  in  Portland 

£ 

Parts 

« 

Mortar. 

tf 

ti        K 

Cement. 

One 

0 

(2  ' 

Cement. 

0 

1 

2 

3 

4 

1 

R 

An 

3 

3  mo. 

162  X 

173  X 

177  X 

162  J 

127  J 

2' 

R 

Gn 

3 

* 

147  X 

175  X 

167  X 

156 

151 

3 

A 

En 

3 

« 

l.->6  X 

157  X 

143  X 

136  X 

134 

4 

G 

Bn 

3 

' 

88  X 

106  X 

115  X 

94 

91  J 

5 

R 

An 

3 

lyr. 

214 

206  X 

206  X 

201  X 

183  J 

6 

R 

Gn 

3 

t 

167  N 

165  X 

180  X 

175  X 

169 

7 

A 

En 

3 

« 

157  N 

158  X 

173  X 

166  X 

160 

8 

G 

Bn 

3 

4 

.108  J 

127  J 

126,1 

130  J 

114  J 

NOTES:  —  In  general,  each  result  is  mean  of  ten  briquets. 

Results  marked  N,  briquets  broke  through  the  natural  cement. 
Results  marked  J,  briquets  broke  at  juncture  of  Portland  and 
natural. 

The  small  blocks  were  made  one  inch  square  and  about 
one-fourth  inch  thick,  two  opposite  edges  of  each  piece  being 
very  slightly  hollowed  to  fit,  approximately,  the  side  of  the 
mold.  These  blocks  being  placed  transversely  in  the  center  of 
the  mold,  and  the  ends  of  the  latter  filled  with  the  mortar  to 
be  tested,  formed  two  joints  between  the  mortar  and  the  block. 

402.  Table  114  shows  the  adhesion  of  a  rich  Portland  ce- 
ment mortar  to  various  materials.  The  mortar  adheres  most 
strongly  to  brick,  the  adhesion  exceeding  the  strength  of  the 
brick  itself.  A  very  high  result  is  also  obtained  with  terra 
cotta,  and  the  adhesion  to  Kelleys  Island  limestone  is  high. 
The  latter  is  a  dolomitic  limestone  of  the  corniferous  group, 
which  is  soft  enough  to  be  worked  quite  easily.  The  adhesion 


274 


CEMENT  AND  CONCRETE 


to  Drummond  Island  limestone,  which  is  a  much  harder  stone 
belonging  to  the  Niagara  group,  is  considerably  less,  and  the 
adhesion  to  the  Potsdam  sandstone  is  very  low,  A  higher  re- 
sult than  would  be  expected  is  obtained  with  ground  plate 
glass,  but  the  hammered  bar  iron  gives  the  lowest  result  of  any 
of  the  substances  tried. 

TABLE    114 
Adhesion  of  Portland  Cement  Mortar  to  Various  Materials 


w 

o 

a 

o 

ADHESION,  POUNDS  PER  SQUARE  INCH, 

X 

K 

KIND 

oj  ®  H 

AGE 

OF 

|| 

TO  MATERIALS. 

m 

OF 

SAND 

•<  H  S 

SPECI- 

h 

P^  S.S 

MENS. 

ti 

^ 

er 

a 

b 

c 

d 

e 

f 

0 

1 

Cr.  Qtz.  20-30 

1 

28  days 

742 

91 

78 

211 

100 

241 

223 

290 

2 

u                 u 

1 

6  inos 

775 

103 

122 

201 

252 

284 

310 

395 

NOTES:  — Cement,  Portland,  Brand  R. 

Adhesion  Blocks,    1  in.  X    1  in.  x  £  in.  inserted  in  center  mold. 
Materials:  —  a  —  Hammered  bar  iron. 

b  —  Potsdam  sandstone,  c'eavage  surface. 

c  —  Drummond  Id.  limestone,  cleavage  surface. 

d  —  Ground  plate  glass. 

e  —  Kelleys  Id.  limestone,  sawn  surface. 

/  —  Soft  terra  cotta,  filed  surface. 

g  —  Soft  red  building  brick,  sawn  surface. 

403.  The  Adhesion  of  Neat  and  Sand  Mortars.  —Table  115 
shows  the  cohesive  and  adhesive  strengths  of  different  mortars, 
the   adhesion   blocks   being   all   of  the   same   material,  Kelleys 
Island  limestone.     The  Portland  mortar  giving  the  highest  ad- 
hesive strength  at  six  months  is  that  containing  one-half  part 
sand  to  one  part  cement,  though  the  greatest  cohesive  strength 
is  given  by  the  one-to-one  mortar.     With  natural  cement  the 
one-to-one  mortar  gives  the  highest  strength,  both  in  adhesion 
and  cohesion.     The  ratio  of  the  adhesive  strength  to  the  co- 
hesive strength  is  greater  for  natural  than  for  Portland.     It 
also  appears  that  between  twenty-eight  days  and  six  months 
the  adhesive  strength  increases  more  than  the  cohesive  strength. 

404.  Effect  of  Consistency  on  Adhesion.  — Table  116  gives 
the  results  of  tests  to  show  the  relative  effects  of  the  consis- 
tency of  the  mortar  on  the  adhesive  and  cohesive  strength,     It 


EFFECT  OF  CONSISTENCY 


275 


TABLE   115 
Adhesion  of  Mortars  Containing  Different  Amounts  of   Sand 


COHESIVE  OR  ADHESIVE  STRENGTH,  LBS. 

I 

CEMENT. 

AGE 

COHESION 

PER  SQUARE  INCH,  OF  MORTARS  WITH 
SAND,  PARTS  BY  WEIGHT. 

pg 

2 

SPECI- 

OK 

ADHESION. 

a 
A 

Kind. 

Brand. 

None. 

Half  Part 
Sand. 

One  Part. 

Two 
Parts. 

1 

Port. 

R 

28  days 

Cohesion 

686 

710 

747 

467 

2 

u 

" 

»» 

Adhesion 

270 

233 

221 

169 

3 

u 

4* 

6  H10S. 

Cohesion 

(581 

787 

816 

551 

4 

u 

'• 

It 

Adhesion 

335 

346 

287 

209 

5 

Nat, 

An 

28  days 

Cohesion 

183 

198 

218 

186 

6 

u 

" 

u 

Adhesion 

94 

104 

116 

66 

7 

" 

'• 

6  inos. 

Cohesion 

203 

334 

383 

376 

8 

" 

'  ' 

u 

Adhesion 

228 

222 

233 

171 

NOTES  :  —  Sand,  crushed  quartz,  20  to  30. 

Adhesion  blocks,  1  in.   X  1  in.   x  ^  in.,  Kelleys  Id.  limestone,  sawn 
surface,  saturated  before  used. 

is  seen  that  the  effect  of  consistency  on  the  adhesive  strength 
is  less  than  on  the  cohesive  strength,  but  that  the  best  results 
in  adhesion  are  given  by  a  mortar  that  is  considerably  more 
moist  than  that  which  gives  the  highest  strength  in  cohesion. 
The  practical  bearing  of  this  point  on  the  use  of  mortars  is  evi- 
dent. 

TABLE    116 
Adhesion  of  Mortars.    Varying  Consistency 


COHESIVE  OR  ADHESIVE  STRENGTH,  LBS. 

a 

g 

u 

CEMENT. 

AGE 

OP 

COHESION 

PER  SQUARE  INCH,  MORTAR  OF 
CONSISTENCY: 

K 

a 

h 

SPECI- 

OR 

ADHESION. 

3 

MENS. 

Trifle 

Trifle 

Quite 

Very 

PH 

Kind. 

Brand. 

Dry. 

Moist. 

Moist. 

Moist. 

1 

Port. 

R 

28  days 

Cohesion 

541 

502 

443 

372 

2 

i 

»t 

Adhesion 

148 

1(50 

14--) 

136 

3 

« 

6  inos. 

Cohesion 

697 

660 

616 

539 

4 

' 

ti 

Adhesion 

191 

209 

228 

192 

5 

Nat. 

An 

28  days 

Cohesion 

239 

212 

151 

112 

6 

' 

K 

Adhesion 

96 

96 

87 

70 

7 

i 

6  inos. 

Cohesion 

397 

385 

314 

285 

8 

i 

it 

Adhesion 

146 

165 

164 

126 

NOTES:  —  Sand,"  Point  aux  Pins,"  pass  No. 10  sieve,  one  part  to  one  cement 

by  weight. 

Adhesion   blocks,    1  in.    X    1  in.   X  i  in.,    Kelleys  Id.  limestone, 
surfaces  filed  smooth,  saturated  with  water  before  used. 


27G 


CEMENT  AND  CONCRETE 


405.  Effect  of  Regaging  on  Adhesive  Strength.  —  The  tests 
given  in  Table  117  were  designed  to  show  the  effect  of  regaging 
on  the  adhesion  of  cement  mortar  to  stone.  A  comparison  is 
made  between  mortars  used  fresh  and  those  that  were  allowed 
to  stand  three  hours  and  gaged  once  an  hour.  There  are  but 
few  tests  from  which  to  draw  conclusions  and  the  treatment  is 
very  severe,  but  it  appears  that  while  the  regaging  to  which 
these  mortars  were  subjected  usually  resulted  in  a  slight  in- 
crease in  cohesive  strength,  the  adhesive  strength  was  consid- 
erably impaired.  The  decrease  in  adhesive  strength  was  greater 
for  natural  cement  than  for  Portland,  and  greater  for  rich  than 
for  poor  mortars.  The  effect  of  regaging  on  the  cohesive  strength 
is  treated  in  Art.  47. 

TABLE   117 
Effect  of  Regaging  on  Adhesive  Strength 


CEMENT. 

ADHESION  OR 
COHESION. 

ADHESION  OR  COHESION,  LBS.  PER  SQ.  IN. 

ONE  PART  SAND  TO  ONE 
CEMENT. 

THREE  PARTS  SAND  TO 
ONE  CEMENT. 

Fresh. 

Regaged. 

Fresh. 

Regaged. 

Portland,  Brand  X 

Adhesion 

178 

141 

62 

41 

44                    4;          u 

44 

202 

170 

51) 

61 

44                   44         (4 

Cohesion 

718 

764 

327 

343 

Natural,        "      An 

U                             44              44 

Adhesion 

44 

142 
180 

90 
120 

17 
31 

28' 

(4                             it              44 

Cohesion 

352 

361 

235 

227 

NOTES:  —  Sand,  crushed  quartz,  |§.  Each  result,  mean  of  two  to  five  speci- 
mens, broken  at  age  of  six  months. 

In  adhesive  tests,  pieces  Kellcys  Id.  limestone,  1  in.  X  1  in.  X  i  in., 
placed  in  center  mold  and  two  ends  mold  filled  with  mortar. 

Results  in  columns  headed  "Fresh"  from  mortar  treated  as  usual. 

Results  in  columns  headed  ''Regaged"  mortar  allowed  to  stand 
three  hours  before  use,  mortar  being  regaged  each  hour. 

406.  Character  of  Surface  of  Stone.  —  In  the  tests  recorded 
in  Table  118  all  of  the  adhesion  blocks  were  of  Kelleys  Island 
limestone,  but  part  of  them  were  finished  with  smooth  filed 
surfaces,  while  the  others  were  grooved  with  a  coarse  rasp.  In 
the  twenty-eight-day  tests  there  is  but  little  difference  in  the 
adhesion  to  the  different  surfaces,  but  at  six  months  the  adhe- 
sion to  the  smooth  surfaces  appears  to  be  slightly  greater,  ex- 
cept in  the  case  of  one-to-two  natural  cement  mortar. 


EFFECT  OF  PLASTER  PARIS 


277 


TABLE  118 
Adhesion  of  Mortars.      Effect  of  Character  of  Surface  of  Stone 


COHESION  OB  ADHESION 

AND 

CHAHACTKK  OF  SURFACE. 

AGE  OF 
SPECIMENS. 

ADHESION  OR  COHESION, 
LBS.  PER  SQ.  IN. 

Portland  Brand  R. 

Natural  Brand  D. 

PARTS  SAND  TO  ONE  CEMENT. 

1 

2 

1 

2 

Cohesion 

28  days 
u 
ti 

6  inos. 

it 

539 
151 
152 
714 
238 
223 

377 
85 
115 
503 
176 
154 

343 
138 
129 
387 
141 
115 

289 
113 
J>8 
304 
68 
96 

Adhesion,  smooth  surface  .     . 
"         grooved  surface 
Cohesion 

Adhesion,  smooth  surface  .     . 
"          grooved  surface 

407.  The  Effect  of  Plaster  of  Paris  on  the  Adhesion  of  Mortar 
to  Stone. — The  results  in  Table  119  show  the  effect  on  the 
adhesive  strength  of  adding  small  percentages  of  plaster  of 
Paris  to  cement  mortars  of  Portland  and  natural  cement.  The 
Portland  cement  used  was  a  quick  setting  sample,  neat  cement 
pats  of  which  began  to  set  in  eighteen  minutes.  The  effect  of 
plaster  of  Paris  on  the  cohesive  strength  of  mortars  from  these 
samples  hardened  in  dry  air,  is  shown  in  Table  92,  §  378.  It  is 
seen  that  the  addition  of  from  one  to  three  per  cent,  plaster 

TABLE   119 

Effect  of  Plaster  of  Paris  on  the  Adhesive  Strength  of  Cement 

Mortars 


ADHESIVE  STRENGTH,   LBS.   PEK 

KEF. 

CEMENT. 

PARTS  P.P. 
SAND  TO 
ONE 

AGE  OF 
SPECIMENS. 

SQ.  IN.,  OF  MORTARS  IN  WHICH 
PER  CENT.  OF  CEMENT  REPLACED 
BY  PLASTER  OF  PARIS. 

Kind. 

Brand. 

Sample. 

CEMENT. 

0 

1 

2 

3 

6 

1 

Port. 

R 

26  R 

0 

1  year 

263 

311 

376 

291 

81) 

2 

<•' 

U 

" 

2 

K 

130 

107 

144 

157 

34 

3 

Nat. 

An 

L 

0 

n 

88 

97 

87 

133 

a 

4 

u 

An 

it 

2 

u 

64 

74 

89 

82 

93 

NOTES:  —  Adhesion  pieces  between  two  halves  of  briquet  were  of  Kelleys  Id. 

limestone,  sawn  surfaces,  saturated  with  water  before  used. 
Cement  and  plaster  Paris  passed  through  No.  50  sieve. 
All  briquets  stored  in  tank  in  laboratory. 
Each  result,  mean  of  four  to  ten  briquets. 

a  Found  badly  cracked  and  separated  from  limestone  prisms  after 
three  days. 


•278  CEMENT  AND  CONCRETE 

has  no  deleterious  effect  on  the  adhesive  strength  of  these 
samples  at  one  year.  Six  per  cent,  plaster,  however,  ruins  the 
Portland  and  the  neat  natural  cement. 

408.  THE  ADHESION  OF  CEMENT  MORTAR  TO  BRICK.  — 
Tests  of  the  adhesion  of  cement  mortar  to  brick  were  made  by 
cementing  pairs  of  brick  in  a  cruciform  shape,  with  a  one-fourth 
inch  joint  of  mortar.     The  brick  were  placed  together  flatwise, 
with  the  bed  down,  so  that  in  the  case  of    stock    brick,  one 
stock  mark,  or  depression  in  one  side,  was  filled  with  mortar. 
The  mortar  was  made  more  moist  than  was  ordinarily  used  for 
briquets,  but  not  so  moist  as  would  be  used  in  brickwork.     The 
top  brick  of  each  pair  was  slightly  tapped  to  place  with  the 
handle  of  a  pointing  trowel,  and  the  excess  mortar  cut  away. 
About  forty-eight  hours  after  cemented,  the  pairs  of  brick  were 
packed  in  damp  sand  in  a  large  box  prepared  for  the  purpose, 
and  the  sand  was  kept  in  a  moist  condition  by  a  thorough  daily 
sprinkling.     For  pulling  the  bricks  apart,  a  special  clip  was  de- 
vised to  equalize  the  pull  on  the  two  ends  of  each  brick,  and  a 
simple  lever  machine  was  used  to  measure  the  force  required. 

409.  Tensile    tests    were    made    of    briquets    from    mortars 
similar  to  those  used  in  the  adhesive  tests  and  stored  in  damp 
sand,  and  the  results  are  used  for  comparison  with  the  adhesive 
tests.     The    cohesive   strength   given   by   the    briquets   is    not 
strictly  comparable  with  the  adhesive  strength  shown  in  the 
tests  with  brick,  because  of  the  great  difference  in  the  area  of 
the  breaking  sections  in  the  two  cases.     It  has  been  well  estab- 
lished in  tensile  tests  of  cohesion  that  briquets  of  large  cross- 
section  break  at  a  lower  strength  than  those  of  small  section. 
It  is  quite  possible  also  that  even  with  the  special  clip  devised, 
cross-strains  were   more  likely  to  occur  in  the   adhesive  tests 
than  in  the  briquet  tests.     An  opportunity  was  furnished  of 
comparing  the  tensile  strength  of  neat  natural  cement  mortar 
under  the  two  conditions,  for  in  one  case  six  joints  broke  di- 
rectly through  the  mortar,  the  adhesion  being  greater  than  the 
cohesion.     It   was   found   that   the   strength   per   square   inch 
given  by  the  briquets  was  at  least  six  times  that  given  by  the 
large  joint.     This  difference  should  be  kept  in  mind  in  making 
comparisons  in  the  tables  between  the  cohesion  and  adhesion 
as  given.     It  should  also  be  noted  that  some  of  the  highest 
results  of  adhesive  strength  represent   in  reality  the  strength 


ADHESION   TO  BRICK 


279 


of  the  brick  rather  than  the  adhesive  strength  of  the  mortar,  as 
chips  were  pulled  from  the  brick,  leaving  the  mortar  joint 
undisturbed.  The  brick  were  of  a  rather  poor  quality,  but 
selected  with  a  view  to  obtaining  those  of  a  uniform  degree  of 
burning. 

TABLE   120 

Adhesion  of  Cement  Mortar  to  Brick.     Variations  in  Richness 

of  Mortar 


TENSILE  STKENGTH,  POUNDS  PER 

SQUARE  INCH,  OF  MORTARS  CONTAINING 

OKMENT. 

AGE  OP 

ADHESION 

OR 

PAHTS  SAND  TO  ONE  CEMENT. 

Mo  UTAH. 

COHESION. 

None. 

I 

1 

2 

3 

Portland,  X,  41  S 

28  days 

Cohesion 

632 

596 

589 

409 

270 

U                       I               ( 

t  i 

Adhesion 

48 

42 

24 

20 

11 

u              t          » 

3  months 

Cohesion 

676 

728 

694 

423 

325 

a              i          i 

(« 

Adhesion 

64 

52 

41 

24 

12 

t;              i         ( 

6  months 

Cohesion 

723 

764 

679 

52  1 

374 

U                     I              i 

U 

Adhesion 

60 

66 

39 

20 

14 

Natural,  Gn,  KK 

3  months 

Cohesion 

180 

240 

317 

279 

181 

U                    U            It 

tt 

Adhesion 

46 

62 

42 

28 

15 

U                    U             U 

6  months 

Cohesion 

276 

444 

388 

331 

236 

4  '               "         " 

it 

Adhesion 

44 

52 

50 

38 

18 

NOTES:  — Bricks  were  cemented  together  in  pairs  in  cruciform  shape  and 

kept  in  damp  sand  until  time  of  test.     Briquets  for  cohesion 

tests  stored  in  same  manner. 
Each  result  in  cohesion,  mean  of  five  briquets. 
Each  result  in  adhesion  is  in  general  mean  of  six  results,  three 

with  common  die  cut  brick  and  three  with  sand  molded  stock 

brick. 
When  adhesion  exceeded  50  pounds  per  square  inch,  bricks  were 

about  as  likely  to  break  as  the  joint  between  brick  and  mortar. 

410.  Adhesion  of  Neat  and  Sand  Mortars  of  Portland  and 
Natural.  —  Some  of  the  results  of  these  tests  are  given  in  Table 
120.  The  most  noteworthy  point  developed  is  that  for  mor- 
tars containing  more  than  one-half  part  of  sand  to  one  part 
cement,  the  adhesion  of  the  natural  cement  is  greater  than 
that  of  the  Portland  with  the  same  proportion  of  sand,  al- 
though the  Portland  mortar  was  much  the  stronger  in  cohesion. 
The  mortars  giving  the  highest  adhesive  strength  are  those 
containing  not  more  than  one-half  part  sand  to  one  part  cement. 

The  addition  of  sand  lowers  the  adhesive  strength  more 
rapidly  than  it  does  the  cohesive  strength.  This  point  would 


280 


CEMENT  AND  CONCRETE 


be  shown  still  more  clearly  if  the  true  adhesive  strength  of  the 
richest  mortars  was  obtained,  as  we  may  be  certain  that  the 
adhesion  of  these  mortars  would  be  shown  to  be  considerably 
greater  if  the  brick  were  strong  enough  to  allow  this  strength 
to  be  developed.  With  natural  cement  mortars  containing  not 
more  than  two  parts  sand  to  one  cement,  the  adhesion  is  one- 
sixth  to  one-ninth  the  cohesion,  and  with  Portland  mortars 
containing  not  more  than  one  part  sand,  the  adhesion  is  about 
one-fifteenth  the  cohesion.  (But  see  §  409  in  this  connection.) 

411.  Effect  of  Lime  Paste  on  Adhesive  Strength  of  Cement 
Mortars.  —  A  number  of  tests  were  made  to  determine  the 
effect,  on  the  adhesive  and  cohesive  strength  of  mortars,  of 
mixing  lime  paste  with  the  cement.  Tables  121  and  122  give 
the  results  of  a  few  preliminary  tests  on  this  subject. 

For  the  tests  recorded  in  Table  121  the  mortars  were  al- 
lowed to  harden  in  dry  air.  From  the  cohesive  tests  it  is  seen 
that  lime  in  form  of  paste  to  the  amount  of  ten  per  cent,  of 

TABLE   121 

Adhesion  of  Cement  Mortar  to  Brick.     Effect  of  Lime  Paste  in 
Mortar  Hardened  in  Dry  Air 


CEMENT. 

AGE 

OF 

MORTAR. 

COHESION 

OB 

ADHESION. 

TENSILE  STRENGTH,  POUNDS  PER 
SQUARE  INCH. 

Composition  of  Mortar. 

A 

B 

C 

D 

E 

Portland,  X,  41S 

It                    it         it 

3  months 
4      " 

Cohesion 
Adhesion 

97 
18 

99 
29 

101 
20 

46 

22 

59 
13 

it                    It         U 

6      " 

a 

24 

20 

19 

11 

Natural,  Gn,  LL 

3      " 

Cohesion 

18 

38 

21 

22 

68 

U                     U             it 

4      " 

Adhesion 

39 

32 

30 

28 

11 

U                     it            it 

6      " 

U 

26 

31 

25 

27 

NOTES:  —  Brick,  sand  molded  stock. 

All  briquets  and  brick  stored  in  dry  air. 

Composition  of  mortars:  A         B        C       D      E 

Grams  P.  P.  river  sand,  480     480     480     480     480 

Grams  cement,  120     120       90       60         0 

Grams  lime  paste,  0       40       30       60     120 

Grams  lime  contained  in  lime  paste,  0       14       10       20       41 
Lime  in  paste  expressed  as  per  cent, 
of  cement  plus  lime, 


0       10       10       25     100 


Consistency  about  same  as  mason's  mortar. 


EFFECT  OF  LIME  PASTE 


281 


the  cement  had  little  effect  on  one-to-four  Portland  mortars, 
but  that  a  larger  amount  of  lime  was  very  deleterious  for  dry 
air  exposure.  The  sample  of  natural  cement  used  did  not  harden 
well  in  dry  air,  and  the  highest  result  is  given  by  the  lime  mor- 
tar without  cement.  It  appears  that  the  adhesive  strength  of 
the  Portland  mortar  was  slightly  increased  by  the  addition  of  a 
small  amount  of  lime  paste,  but  the  adhesive  strength  of  natural 
was  not  greatly  affected.  The  adhesive  strength  of  the  natural 
cement  is,  in  general,  higher  than  the  Portland.  The  nat- 
ural cement  appeared  to  harden  better  in  the  joints  than  in  the 
briquets,  and  we  have,  as  a  peculiar  result,  the  adhesive  strength 
exceeding  the  cohesion.  This  illustrates  a  statement  already 
made,  that  to  store  briquets  in  dry  air  does  not  approach  very 
nearly  the  ordinary  conditions  of  use. 

412.    In  Table  122  are  given  a  few  tests  of  mixtures  of  Port- 

TABLE   122 

Adhesion    of   Cement  Mortar   to    Brick.     Effect   of  Lime   Paste   in 
Portland  Cement 


TENSILE  STRENGTH,  POUNDS  PER  SQUARE  INCH. 

MORTAR  HARDENED  IN 

COHESION 

OR 

COMPOSITION  OF  MORTAR. 

ADHESION. 

A 

B 

C 

D 

E 

Tank  in  Laboratory 

Coh'n. 

177 

203 

183 

158 

82 

Dry  air, 

(i 

167 

180 

167 

150 

81 

Damp  sand,    " 

« 

173 

198 

171 

154 

88 

Dry  air, 

Adh'ii. 

15 

36 

40 

33 

26 

Damp  sand,    " 

it 

15 

33 

35 

32 

27 

NOTES:  —  Bricks  cemented  together  in  pairs  in  cruciform  shape. 

Age  of  all  mortars  when  tested,  three  months. 

Cement,  Portland,  Brand  R,  Sample  14  R.  Sand,  "  Point  aux  Pins." 

Lime  paste  slaked  about  six  months  before  use. 

Each  result  in  cohesion,  mean  of  five  to  ten  briquets. 

Each  result  in  adhesion,  mean  of  eight  to  sixteen  pairs  of  bricks. 

Half  of  pairs  were  hard  burned  brick  and  half  soft  burned. 

Composition  of  mortars:  A       B       C       D       E 

Grams  P.  P.  (river)  sand,  960     960     960     960     960 

Grams  cement,  240     240     200     180     120 

Grams  lime  paste,  0      80     120     180     360 

Grams  lime  contained  in  paste,  0       27       40       60     120 

Lime  as  per  cent,  lime  plus  cement,          0       10     16.7       25      50 


282  CEMENT  AND  CONCRETE 

land  cement  and  lime  paste,  the  mortars  being  hardened  in  dry 
air  and  in  damp  sand.  Cohesive  tests  are  also  given  of  briquets 
hardened  in  damp  sand,  water  and  dry  air.  It  appears  that 
the  addition  of  ten  per  cent,  of  lime  in  the  form  of  paste  to 
mortars  of  this  sample  of  Portland  increases  the  tensile  strength, 
the  effect  being  least  when  the  mortars  harden  in  dry  air.  The 
substitution  of  lime  for  one-sixth  of  the  cement  in  a  one-to-four 
mortar  has  little  effect  on  the  tensile  strength.  Larger  propor- 
tions of  lime  result  in  decreased  strength,  and  if  one-half  of  the 
cement  is  replaced  by  lime,  the  resulting  strength  is  only  about 
one-half  that  given  by  the  cement  mortar  without  lime.  The 
results  of  the  adhesive  tests  show  that  if  half  of  the  cement  in 
the  mortar  is  replaced  by  an  equal  weight  of  lime  in  the  form 
of  paste,  the  resulting  strength  is  increased  by  nearly  100 
per  cent.,  and  that  if  smaller  amounts  of  lime  are  used,  the 
adhesive  strength  is  increased  by  about  150  per  cent,  over 
that  given  by  the  cement  mortar  without  lime. 

413.  The  results  of  a  more  complete  set  of  tests  on  this  sub- 
ject'are  given  in  Table  123.  The  mortars  used  included  one 
made  with  four  parts  sand  to  one  of  cement  by  weight;  one  in 
which  about  ten  per  cent,  of  lime  by  weight,  which  had  pre- 
viously been  made  into  lime  paste,  was  added  to  the  mortar;  a 
third  in  which  lime,  in  the  form  of  paste,  was  substituted  for 
one-sixth  of  the  weight  of  the  cement  used  in  the  first  mortar; 
a  fourth,  in  which  lime  was  substituted  for  one-fourth  of  the 
cement;  and  finally,  a  mortar  composed  of  lime  paste  and  sand 
only. 

The  adhesive  strengths  of  the  mortars  are  given  in  the 
table.  The  difference  in  the  adhesion  of  Portland  cement 
mortar  to  hard  brick  and  to  soft  brick  is  not  clearly  brought 
out.  Neither  is  the  strength  of  air-hardened  specimens  much 
different  from  that  of  the  mortars  stored  in  damp  sand.  The 
use  of  lime  paste  with  Portland  cement  in  the  amounts  tried 
here  more  than  doubles  the  adhesive  strength  of  the  mortar. 

The  first  point  to  notice  in  the  case  of  natural  cement  is 
that  the  adhesive  strength  of  this  mortar  without  lime  is  nearly 
double  the  adhesive  strength  of  Portland  mortar  without  lime. 
The  adhesive  strength  of  mortars  hardened  in  damp  sand  is 
somewhat  greater  than  the  strength  of  similar  mortars  hard- 
ened in  dry  air.  The  addition  of  a  small  amount  of  lime  paste 


EFFECT  OF  LIME  PASTE 


283 


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284  CEMENT  AND  CONCRETE 

increases  the  adhesive  strength  somewhat,  and  when  as  much 
as  twenty-five  per  cent,  of  the  cement  is  replaced  by  lime  in 
the  form  of  paste,  the  adhesive  strength  of  the  natural  cement 
mortar  is  not  usually  diminished.  The  effect  of  lime  paste, 
however,  on  the  adhesive  strength  is  not  nearly  so  great  as  it 
is  in  the  case  of  Portland  mortars. 

The  following  conclusions  may  be  briefly  stated:  The  ratio 
of  adhesive  to  cohesive  strength  is  much  greater  with  natural 
cement  than  with  Portland.  If  a  high  adhesive  strength  is 
desired,  Portland  cement  should  not  be  mixed  with  more  than 
two  parts  sand  unless  lime  paste  is  added  to  the  mortar,  as 
the  use  of  lime  paste  materially  increases  the  adhesive  strength 
of  lean  mortars.  Tests  of  cohesion  of  similar  mortars  contain- 
ing lime  paste  are  given  in  Art.  48. 

414.  THE  ADHESION  OF  CEMENT  TO  RODS  OF  STEEL  AND 

IRON.  —  The  tests  recorded  in  Tables  124  and  125  were  made 
to  determine  the  adhesion  of  cement  mortar  to  iron  rods,  or 
the  strength  of  a  bolt  anchorage  secured  with  cement  mortar, 
and  the  style  of  rod  and  kind  of  mortar  which  would  give  the 
best  results.  The  bars  were  made  in  an  ordinary  concrete 
mold,  ten  inches  by  ten  inches  by  four  and  one-half  feet.  The 
rods  or  bolts  were  placed  in  a  row  along  the  center  of  the  box, 
being  spaced  about  nine  inches  apart,  and  the  mortar  was 
rammed  about  them.  After  being  allowed  to  set  in  a  warm 
room  for  twenty-eight  days,  the  rods  were  pulled  by  means  of 
two  hydraulic  jacks,  a  special  grip  being  used  to  grasp  the  free 
end  of  the  rod,  and  an  hydraulic  weighing  machine  serving  to 
measure  the  pull  required  to  start  it.  The  supports  against 
which  the  hydraulic  jacks  were  braced  bore  at  points  on  the 
concrete  bar  about  three  or  four  inches  from  the  center  of  the 
rod  which  was  being  tested. 

415.  The  rods  given  in  Table   124  were  imbedded  in  mortar 
composed  of  one  part  of  Portland  cement  to  two  parts  lime- 
stone screenings.     The  rods  were  cut  from  bar  iron  and  were 
perfectly  plain,  without  nuts  or  fox  wedges.     The  results  in- 
dicate that  the  force  required  is  proportional  to  the  area  of 
contact.     Comparing  the  different  styles  and  sizes  of  plain  rods, 
no  difference  in  favor  of  one  style  or  size  can  be  determined; 
the  apparent  higher  resistance  per  square  inch  offered  by  one- 
inch  rods  would  probably  disappear  in  a  large  number  of  tests. 


ADHESION   TO  STEEL  RODS 


285 


TABLE  124 

Resistance  to  Pulling  of  Iron  Rods   of  Various   Forms   Imbedded 

in  Mortar 


§ 

POUNDS  PULL. 

PERIM- 

DEPTH 

REF. 

gg 
«  o 
SK 
p 

MORTAR, 
BAR  No. 

DESCRIPTION  OF  Ron. 

ETER 
OF  ROD, 
INCHES. 

IM- 
BEDDED, 
INCHES. 

Per  In. 
Depth 
Im- 

PerSq. 
In.  Area 
in  Con- 

Z 

bedded. 

tact. 

1 

3 

2,  6,  7 

Plain,  i  '  diameter 

1.57 

8  to  10 

700 

447 

2 

3 

i* 

V 

3.14 

" 

1750 

556 

3 

3 

i  < 

H' 

3.03 

u 

2060 

524 

4 

3 

(i 

^   square 

2.00 

11 

1085 

543 

;"> 

4 

2,5,6,7 

r        " 

4.00 

u 

22oO 

5(52 

<l 

3 

2,  6,  7 

iy      » 

5.00 

it 

2170 

434 

7 

3 

4,  5 

I  Twisted  1"  square,    j 
I  1  turn  in  8"  length    ( 

4.31 

o± 

25D5 

608 

8 

3 

t{ 

(  Twisted  1"  square,    \ 
1  2  turns  in  8"  length  J 

4.31 

9± 

2215 

516 

1) 

3 

11 

{  Twisted  1"  square,    ( 
j  3  turns  in  8"  length  j 

4.31 

0-9.5 

2405 

561 

NOTES:  — Cement,  Portland,  Brand  R. 

Sand,  limestone  screenings  passing  f    inch  slits,  two  parts  by 

weight  to  one  cement. 
Mortar  one  month  old  when  tension  was  applied  to  rods. 

The  rods  given  in  lines  seven  to  nine  were  made  by  twisting 
a  piece  of  one  inch  square  bar  iron.  The  twisted  portion  was 
eight  inches  in  length.  Comparing  the  plain  one  inch  square 
bolts  with  the  twisted  bolts,  it  appears  that  the  former  offered 
a  resistance  of  2,245  pounds  per  inch  depth  while  the  latter 
gave  2,405  pounds,  an  increase  of  less  than  eight  per  cent. 

416.  In  the  tests  recorded  in  Table  125,  the  ordinary  river 
sand  used  in  construction  was  employed.  The  mortar  was 
made  neat  and  with  two  and  four  parts  sand  to  one  of  cement. 
The  depth  the  rods  were  imbedded  varied  from  two  inches  to 
ten  inches.  The  one-to-two  mortar  gave  nearly  as  good  results 
as  neat  cement,  but  the  one-to-four  mortar  gave  much  lower 
results.  The  resistance  seems  to  vary  directly  as  the  area  of 
contact  without  reference  to  the  depth  imbedded,  except  as 


1  In  computing  adhesion,  or  shear,  or  pounds  pull  per  square  inch  of  area 
in  contact,  perimeter  considered  circumference  of  a  circle  of  diameter  equal 
to  the  distance  between  opposite  edges  of  rod  after  twisting.  A  core  of  mor- 
tar of  this  diameter,  was  torn  from  bar  in  pulling. 

To  perceive  effect  twisting,  compare  pounds  pull  per  inch  depth  imbedded. 


286 


CEMENT  AND  CONCRETE 


this  enters  in  obtaining  the  said  area.  The  results  obtained  in 
this  table  do  not  compare  favorably  with  those  obtained  in 
Table  124,  where  limestone  screenings  were  used. 

TABLE   125 

Resistance  to  Pulling  of  Iron  Rods  Imbedded  in  Mortar.     Variations 
in  Depth  Imbedded  and  in  Richness  of  Mortar 


PARTS 

SAND  TO 
ONE 
CEMENT. 

ADHESION,  POUNDS  PER  SQUARE  INCH  OF  SURFACE  IN  CONTACT  FOR  DIFFERENT 
DEPTHS  IMBEDDED. 

Depths  ) 
Imbed- 
ded, In  ) 

1.9-2.2 

3*2 

4 

4.5^1.8 

5.8-6 

7.8-8 

8.8 

9.6-10 

No. 
Re- 
sults. 

Mean. 

0 
2 
4 

340 

272 

74 

294 

346 
270 
119 

262 

313 
255 
117 

247* 

100 

228 

340 
275 
142 

5 
15 
10 

313 
264 
111 

NOTES  :  —  Cement,  Portland,  Brand  R. 

Sand,  "Point  aux  Pins,"  river  sand. 
Mortar  one  month  old  when  rods  pulled. 
Rods,  round,  1  inch  diameter. 

417.  Tables  126  and  127  are  from  similar  tests  made  by 
Messrs.  Peabody  and  Emerson.1  The  rods  in  Table  126  were 
of  various  shapes  and  included  some  having  rivets  through 
them.  The  ^  inch  by  1  inch  bars  gave  lower  adhesion  per 
square  inch  than  the  square  and  round  rods.  When  two  rods 
are  twisted  together  and  imbedded  in  a  small  specimen,  the 
tendency  is  to  split  the  specimen.  The  bars  containing  rivets 
broke  before  the  adhesion  was  overcome,  although  the  depth 
imbedded  Was  but  six  inches. 

In  Table  127  neat  cement  paste  and  concretes  of  several 
compositions  are  tried.  These  results  are  of  interest  as  show- 
ing that  concretes  show  as  great  adhesion  to  steel  rods  as  do 
mortars.  The  very  low  result  obtained  with  neat  cement  in 
this  table  is  not  explained  and  is  in  opposition  to  the  results 
in  Table  125. 


Engineering  News,  March  10,  1904. 


ADHESION   TO  STEEL  RODS 


287 


TABLE   126 

Adhesion  of  Mortar  to  Steel  Rods  of  Various  Shapes,  Imbedded 
about  Six  Inches 


No. 

OF 

TESTS. 

DESCRIPTION  OF  ROD. 

PERIMETER 
OF  ROD, 
INCHES. 

POUNDS  PULL. 

Per  Inch 
Depth 
Imbedded. 

Per  Square 
Inch  Area 
in  Contact. 

4 
3 
4 
4 
4 

4 

Plain,  \"  square. 
Plain,  \"  square. 
Plain,  \"  round. 
Twisted,  \"  square. 
V  by  1  ". 

Two  \"  rods  twisted 
together. 

1.0 
2.0 
1.57 

2.5 

369 
864 
804 
1259 
744 

369 
432 
512 

293 

Three  specimens  split. 
One  rod  broke  at  8,000  Ibs.,  or  when 
adhesion  was  1,250  Ibs.  per  inch 
depth. 

4 

\"  by  1"  with  I"  rivets 
through. 

One  specimen  split. 
Three  rods  broke  at  lirst  rivet  with 
9,800  to  10,500  pounds,  or  when 
adhesion  was  1,500  to  1,660  Ibs. 
per  inch  depth. 

NOTES:  —Tests  by  Messrs.  George  A.  Peabody  and  Samuel  W.  Emerson. 

Mortar  composed  of  one  part  cement  (Portland)  to  three  parts  sand. 
Specimens  approximately  6  inch  cubes.      One  rod  imbedded  in 

each,  6  to  6£  inches. 
Rods  pulled  forty  and  eighty  days  after  mortar  was  made. 

TABLE    127 

Adhesion  of  Mortars  and  Concretes  of  Various  Compositions  to 
One  Inch  Square  Steel  Rods  Imbedded  about  Ten  Inches 


COMPOSITION  OF  MORTAR  OR 

POUNDS  PULL. 

No. 

CONCRETE. 

OF 

TESTS. 

Per    Inch 
Depth 
Imbedded. 

Per  Square 
Inch  Area 
in  Contact. 

Cement. 

Sand. 

Stone. 

Gravel. 

4 

0 

0 

0 

1112 

278 

4 

3 

0 

0 

1644 

411 

4 

3 

6 

0 

1912 

478 

4 

3 

0 

6 

2062 

516 

4 

2 

4 

0 

2348 

587 

4 

1 

2 

0 

4 

2187 

547 

NOTE:  —  Tests  by  Messrs.  George  A.  Peabody  and  Samuel  W.  Emerson. 


CHAPTER  XVI 

THE  COMPRESS1VE   STRENGTH   AND   MODULUS  OF 
ELASTICITY   OF  MORTAR  AND   CONCRETE 

ART.  52.     COMPRESSIVE  STRENGTH  OF  MORTAR 

418.  The  compressive  strength  of  cement  mortar  is  from 
five  to  ten  times  the  tensile  strength.  As  the  result  obtained 
in  tests  of  either  compression  or  tension  depends  upon  the  shape 
and  size  of  the  specimen,  no  definite  value  can  be  assigned  to 
the  ratio  of  compression  to  tension.  Comparative  tests  have 
indicated  in  a  general  way  that  the  cements  giving  the  best 
results  in  tension  show  also  the  highest  compressive  strength; 
but  with  variations  in  treatment,  different  kinds  and  brands  of 
cement  do  not  give  the  same  variations  in  the  ratios  of  the  two 
kinds  of  strength. 

Mortar  is  not  usually  employed  alone  in  large  masses.  It 
more  frequently  forms  the  binding  medium  between  fragments 
of  other  substances,  such  as  brick  and  stone.  The  dependence 
of  the  strength  of  masonry  upon  the  strength  of  the  mortar 
increases  with  the  roughness  of  the  stone  or  brick,  and  the 
thickness  of  the  bed  joints.  In  fine  ashlar  masonry  this  depend- 
ence is  comparatively  small,  in  brickwork  it  is  important,  and 
in  concrete  any  increase  in  the  strength  of  the  mortar  increases 
the  strength  of  the  concrete  in  nearly  the  same  ratio. 

Piers  of  brickwork  may  give  a  crushing  resistance  either 
greater  or  less  than  the  strength  of  cubes  made  from  mortar 
of  the  same  composition  as  that  used  in  building  the  piers. 
Thin  beds  of  mortar  between  strong  materials  resist  high  com- 
pressive stresses,  while  in  walls  or  piers  built  with  weak  blocks, 
the  mortar  is  destroyed  by  the  cracking  of  the  blocks  at  a  lower 
stress  than  the  mortar  would  withstand  in  a  cube  pressed 
between  steel  plates.  Since  in  brick  and  stone  masonry  the 
mortar  forms  but  a  small  part  of  the  structure,  it  is  not  econom- 
ical to  use  a  poor  quality  of  mortar  with  good  brick  and  stone. 

288 


CEMENT  MORTAR 


289 


419.   Ratio    of    Compressive    to    Tensile    Strength.  —  M.    E. 

Candlot  has  made  many  experiments  showing  the  effect  of 
certain  variations  in  the  preparation  of  mortars  upon  the  com- 
pressive  and  tensile  strength.  A  few  of  the  results  of  one 
series  are  presented  in  Table  128.  The  reduction  from  the 
metric  system  has  been  made,  and  a  column  added  giving 
approximately  the  number  of  parts  of  sand  to  one  of  cement  by 
weight,  the  accurate  proportions  appearing  in  the  form  of 
weight  of  cement  to  one  cubic  yard  of  sand.  These  results  in- 
dicate that  the  ratio  of  the  strength  in  compression  to  that  in 
tension  increases  with  the  age  of  the  mortar  and  also  with  its 
richness. 

TABLE   128 

Resistance  of  Cement  Mortars  to  Tension  and  Compression,  with 

Varying  Proportions  of  Normal  Sand 

SPECIMENS  HARDENED  IN  FKESH  WATER 

[From  Ciments  et  Chaux  Ifydrauliqucs,  par  M.  E.  Candlot.] 


-SS  8* 

h 

RESISTANCE  IN  POUNDS  PER  SQUARE  INCH  IN  TENSION  AND 

•  §£ 

0^j<  0  H 

*  Q  J 

COMPRESSION. 

«  *  u 

!g.*§* 

J££ 

|H« 

•  Q  H  w^* 

s  s  - 

7  days. 

28  days. 

1  year. 

2  years. 

3  years. 

O  n  w 

O  ^^  §  W 

g  So 

2  ^  E 

KOC   *-*  & 

[^O  ^ 

H  fcH 

l|«£ 

Pi 

T. 

C. 

T. 

C. 

T. 

C. 

T. 

C. 

T. 

C. 

«§5 

10.8 

250 

27 

266 

38 

408 

70 

507 

74 

572 

108 

738 

6.8 

6.4 

420 

128 

643 

143 

1164 

212 

1730 

209 

1630 

219 

1775 

8.1 

4.6 

590 

139 

1040 

234 

1940 

337 

2980 

284 

2930 

341 

3080 

9.0 

3.5 

7(50 

233 

1520 

393 

3080 

435 

4020 

400 

4400 

462 

4590 

9.9 

2.9 

930 

251 

2110 

462 

3690 

490 

5580 

490 

5680 

557 

6060 

10.9 

2.6 

1100 

341) 

2630 

551 

5020 

594 

5820 

557 

6060 

616 

6480 

10.5 

2.0 

1350 

368 

3360 

550 

5020 

713 

7750 

805 

7860 

784 

8710 

11.1 

1.6 

1690 

4  13 

3310 

561 

5070 

767 

7670 

907 

8800 

815 

9180 

11.3 

From  a  study  of  the  results  of  nearly  three  thousand  tests 
made  by  Professor  Tetmajer,  the  late  Professor  J.  B.  Johnson 
concluded  that  for  mortars  containing  three  parts  sand  to  one 
cement  the  ratio  of  the  compressive  strength  to  the  tensile 
strength  is  equal  to  8.64  -f-  1.8  log.  A,  where  A  is  the  age  of 
the  mortar  in  months.  It  is  shown  above  that  the  ratio  in- 
creases with  increasing  proportions  of  sand. 

420.  Table  129  gives  some  results  obtained  at  the  Water- 
town  Arsenal  in  tests  of  cement  mortar  cubes.1  The  mortars 


Prepared  by  Mr.  George  W.  Rafter  for  the  State  Engineer  of  New  York. 


290 


CEMENT  AND  CONCRETE 


TABLE   129 
Compressive  Strength  of  Cement  Mortar.  —  Portland  and  Natural 

TESTS  OF  12  INCH  CUBES,  TWENTY  MONTHS  OLD,  MADE  AT  WATERTOWN 
ARSENAL  FOR  STATE  ENGINEER  OF  NEW  YORK 


METHOD  OF  STORAGE  OF 
CUBES. 

CEMENT. 

CONSISTENCY 

OF 

MORTAR. 

CRUSHING  STRENGTH,  LBS.  PER 
SQUARE  INCH,  FOR  MORTARS 
CONTAINING  PARTS  SAND  TO  ONE 
CEMENT  BY  VOLUME: 

Kind. 

Brand. 

1 

2 

3 

4 

Mean 

f    Dry 

3479 

2200 

1154 

2278 

Water  3  to    4    mo., 
then  buried  in  sand. 

Nat. 

Buffalo 

1  Plastic 
1  Excess 

'2795 
2161 

1783 
1698 

1000 
776 

1859 
1545 

I  Mean 

2812 

1894 

977 

1894 

Covered  with  burlap; 

f    Dry 

3347 

2000  » 

961 

2103 

kept  wet  for  several 
weeks,  then  exposed 

Nat. 

Buffalo 

I  Plastic 
1  Excess 

2476 
2070 

1294  " 
1358 

692 
738 

1487 
1389 

to  weather.      .     . 

[_  Mean 

2631 

1551 

797 

.  .  . 

1660 

{Dry 

2844 

2051 

987 

1961 

In  cool  cellar 

Nat. 

Buffalo 

Plastic 

2514 

1256 

883 

!  ! 

1551 

Excess 

2159 

1386 

678 

1408 

Mean 

2504 

1564 

849 

. 

1640 

Fully     exposed     to 
weather 

Nat. 

Buffalo 

C    Dry 
!  Plastic 

3272 

2667 

1879 
1356 

1054 
822 

2068 
1615 

1  Excess 

1996 

1311 

669 

1325 

I  Mean 

2645 

1513 

848 

1669 

f    Dry 

3236 

2032  2 

1039 

2102 

Means  

^  Plastic 

2613 

1421 

849 

. 

1628 

[  Excess 

2097 

1438 

715 

.  .  . 

1417 

Grand  mean      .     . 

2649 

1630 

868 

1716 

Water    3  to  4  mo., 
-then  buried  in  sand 

Port. 

Empire 

f    Dry 

\  Plastic 

.  .  . 

3897 
3642 

2494 

2168 

1782 
1717 

.   .  . 

Covered  with  burlap; 

kept  wet  for  several 

weeks,  then  exposed 
to  weather. 

Port. 

Empire 

f    Dry 
|  Plastic 

. 

3880 
3672 

2492 
2168 

1489 
1726 

In  cool  cellar     . 
Fully     exposed     to 
weather      .     .     . 

Port. 
Port. 

Empire 
Empire 

Plastic 
Dry 
Plastic 

.  .  . 

3397 
3313 
4059 

3589 

2132 
2164 

2450 
2270 

1614 
1679 
1715 
1465 

.  .  . 

Dry 

3808 

2392 

1650 

Means  

Plastic 

3554 

2193 

1647 

•    • 

contained  one,  two  and  three  volumes  of  sand  to  one  of  natural 
cement,  and  two  to  four  parts  sand  to  one  volume  of  Portland. 


1  Result  interpolated. 

*  2,043  omitting  interpolated  result. 


CONCRETE  291 

The  proportions  of  water  used  were  such  as  to  give  mortars  of 
different  consistency,  "dry,"  like  damp  earth,  "plastic,"  of  the 
consistency  usually  employed  by  masons,  and  "excess,"  quak- 
ing like  liver  with  slight  tamping.  The  specimens  were  twelve 
inch  cubes  and  four  methods  of  storage  were  used,  as  indicated. 

Comparing  the  results  with  similar  tests  of  tensile  strength, 
it  appears  that  the  strength  in  compression  decreases  more 
rapidly  as  sand  is  added  than  does  the  tensile  strength.  The 
same  conclusion  was  drawn  from  Table  128. 

The  strength  of  the  Portland  mortar  with  four  parts  sand 
is  about  equal  to  the  strength  of  the  natural  with  two  parts. 
The  dry  mortar  gives  the  highest  strength  with  natural  cement, 
but  with  Portland  the  "dry"  and  "plastic"  give  about  the 
same  result. 

Concerning  the  consistency,  it  has  already  been  pointed  out 
that  the  conditions  of  the  actual  employment  of  mortar  are 
,  such  as  to  favor,  in  general,  the  use  of  a  wetter  mixture  than 
that  which  gives  the  best  results  in  laboratory  tests  of  mortars. 
As  to  storage,  the  specimens  kept  in  water  for  three  or  four 
months  after  made,  give  the  highest  results  with  natural  ce- 
ment. There  seems  to  be  no  choice  between  the  other  three 
methods  of  storage. 

ART.  53.     COMPRESSIVE  STRENGTH  OF  CONCRETE  WITH  VARIOUS 
PROPORTIONS  OF  INGREDIENTS 

421.  With  the  increasing  use  of  concrete  in  arch  bridges, 
in  foundation  piers  and  in  columns  of  buildings,  and  especially 
in  connection  with  steel  in  beams,  etc.,  the  compressive  strength 
of  the  material  becomes  of  the  greatest  importance.  Moreover, 
the  composition  of  concrete  may  vary  so  much,  the  range  of 
available  aggregates  is  so  wide,  and  the  methods  of  manipula- 
tion are  so  diverse,  that  many  tests  must  be  studied  before 
one  can  judge  of  the  probable  strength  of  a  given  mixture. 

For  any  very  extended  work,  it  may  be  found  economical 
to  make  a  series  of  tests  using  the  materials  available,  and 
combining  them  as  nearly  as  possible  in  the  manner  proposed 
in  actual  construction.  This  practice  has  been  followed  in 
several  important  works,  and  the  data  thus  accumulated  have 
added  much  to  our  hitherto  somewhat  vague  notions  of  the 
probable  strength  of  different  mixtures  under  varying  condi- 


292 


CEMENT  AND  CONCRETE 


tions  of  use.  It  is  possible  here  to  abstract  but  a  few  of  the 
more  reliable  and  complete  tests  of  this  kind,  selecting  those 
which  indicate  the  value  of  certain  special  kinds  of  aggregate 
or  the  effect  of  certain  variations  in  manipulation. 

422.  In  connection  with  the  design  of  the  Boston  Elevated 
R.  R.7  Mr.  George  A.  Kimball,  Chief  Engineer,  prepared  a  series 
of  concrete  cubes  of  mixtures  usually  employed  in  practice, 
and  with  the  materials  available  for  the  work  in  hand,  and  these 
cubes  were  tested  at  the  Watertown  Arsenal  in  1899.  A  por 
tion  of  the  results  of  these  experiments  are  given  in  Table  130, 
where  the  details  concerning  character  of  the  materials  and 
the  preparation  of  the  specimens  are  shown.  As  each  result 
in  the  table  is  the  mean  of  at  least  twenty  specimens,  the  ir- 
regularities frequently  appearing  in  compressive  tests  have 
been  largely  eliminated,  and  the  results  are  worthy  of  much 
confidence. 

TABLE  130 

Compressive   Strength   of  Concrete 
TESTS  OF  12  INCH  CONCRETE  CUBES  FOR  BOSTON  ELEVATED  RAILROAD. 


COMPOSITION  OF  CONCRETE  BY 
VOLUME. 

CRUSHING  STRENGTH,  POUNDS  PER  SQUARE  INCH, 
AT  AGE, 

Cement. 

Sand.  . 

Stone. 

7  days. 

1  month. 

3  mouths. 

6  months. 

1 
1 
1 

2 

3 

0 

4 
6 
12 

1525 
1232 
583 

2440 
2063 
1042 

2944 
2432 
1006 

3904 
29(>9 
1313 

NOTES:  — 

Materials:  —  Cement,  mean  results  with  four  brands  Portland,  two  Ameri- 
can, two  German. 

Sand,  coarse,  clean,  sharp,  voids  33  per  cent,  loose. 
Broken  stone,  conglomerate  passing  2^  inch  ring,  voids  49| 

per  cent,  loose. 

Mixing :  —  Sand  and  cement  turned  twice,  mortar  and  stone  turned  twice. 
Storage :  —  Cubes  removed  from  molds  three  or  four  days  after  made  and 

buried  in  wet  ground  until  about  a  week  before  testing. 
Each  result,  mean  of  twenty  or  more  tests. 

Tests  made  at  Watertown  Arsenal,  for  George  A.  Kimball,  Chief  Engineer, 
Boston  Elevated  R.R.     "Tests  of  Metals,"  1899. 

At  the  time  of  making  these  tests  some  cubes  were  crushed 
with  a  die  having  a  smaller  area  than  the  face  of  the  cube. 


CONCRETE  293 

With  a  die  8  by  8^  inches  on  one  compression  face,  the  area  of 
the  die  being  thus  about  .46  of  the  area  of  the  cube  face,  the 
strength  per  square  inch  under  the  die  was  about  twenty-five 
per  cent,  higher  than  when  the  entire  face  of  the  cube  was 
pressed.  This  is  in  line  with  the  behavior  of  all  brittle  sub- 
stances under  compression,  as  shown  by  Professor  Bauschinger 
in  testing  sandstone  specimens. 

423.  Tables  131  and  132  give  a  summary  of  a  part  of  a  very 
valuable  series  of  tests  of  concrete  cubes  prepared  by  Mr.  George 
W.  Rafter  and  tested  at  the  Watertown  Arsenal  for  the  State 
Engineer  of  New  York.1 

The  results  summarized  in  Table  131  are  those  obtained  with 
four  brands  of  Portland  cement  made  in  the  State  of  New 
York,  namely,  Wayland,  Genessee,  Empire  and  Ironclad.  Tests 
were  also  made  with  a  sand-cement,  and  with  one  brand  of 
natural,  but  these  results  are  not  included  in  the  table.  The 
aggregate  was  sandstone  of  the  Portage  group,  broken  by  hand 
to  pass  a  two  inch  ring. 

The  mortars  used  in  making  the  cubes  were  of  three  degrees 
of  consistency:  (a)  In  the  dry est  blocks  the  mortar  was  only  a 
little  more  moist  than  damp  earth,  and  much  ramming  was 
required  to  flush  water  to  the  surface.  (6)  In  another  set  the 
mortar  was  about  the  consistency  of  ordinary  mason's  mortar, 
(c)  In  the  third  set,  the  mortar  was  wet  enough  to  quake  like 
liver  under  moderate  ramming. 

424.  The  mortar  was  composed  of  one  volume  of  loose  ce- 
ment to  two,  three  or  four  volumes  of  loose  sand.     Other  pro- 
portions were  also  employed,  but  in  this  table  only  those  re- 
sults are  included  in  which  the  series  of  tests  was  complete  as 
to  variations  in  consistency  and  storage. 

The  voids  in  the  stone  were  about  forty-three  per  cent, 
when  the  measure  was  slightly  shaken,  and  thirty-seven  and 
a  half  per  cent,  when  rammed  without  mortar.  The  amount 
of  mortar  used  was  made  either  thirty-three  per  cent,  or  forty 
per  cent,  of  the  volume  of  the  loose  stone. 

Four  methods  of  storage  were  used  as  follows:  1st,  blocks 
immersed  in  water  as  soon  as  they  were  removed  from  the 
molds,  and  after  three  or  four  months  they  were  buried  in  sand; 


1  Report  of  State  Engineer  of  New  York,  1897. 


294 


CEMENT  AND  CONCRETE 


TABLE    131 

Compressive  Strength  of  Concrete 

MEAN  RESULTS  WITH  FOUR  BRANDS  PORTLAND  CEMENT,  ILLUSTRATING  EFFECTS 

OF  PROPORTIONS,  CONSISTENCY,  AND  METHODS  OF  STORAGE.     TESTS  OF 

CONCRETE  CUBES,  ABOUT  TWENTY  MONTHS  OLD,  MADE  FOR 

STATE  ENGINEER  OF  NEW  YORK 


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CONCRETE  295 

2d,  blocks  covered  with  burlap  and  wet  frequently  for  several 
weeks,  after  which  they  were  exposed  to  the  weather;  3d,  kept 
in  a  cool  cellar  from  the  time  of  fabrication  until  shipped  for 
testing,  and  4th,  fully  exposed  to  the  weather  throughout. 

425.  In  Table  131  each  result  is  the  mean  of  four  cubes,  one 
of  each  brand.     The  mean  results  are  so  arranged  as  to  show 
the  effects   of  variations  in  the  amount,  the  richness,  and  the 
consistency  of  the  mortar,  and  of  the  different  methods  of  storage. 

Taking  up  first  the  question  of  consistency,  it  appears  from 
column  "/"  that  the  use  of  plastic  mortar,  marked  " mason's," 
gave  from  92  to  97  per  cent,  of  the  strength  given  by  the  dry 
mortar  of  about  the  consistency  of  "moist  earth;"  and  that 
the  "quaking"  concrete  gave  from  89  to  95  per  cent,  of  the 
strength  of  that  marked  "moist  earth."  From  the  three  lines 
at  the  bottom  of  the  table  it  is  seen  that  in  the  poor  concrete, 
one-to-four  mortar,  the  wettest  mortar  gave  nearly  as  good 
results  as  the  dryest,  while  in  the  rich  concrete,  one-to-two 
mortar,  the  strength  of  the  wet  was  but  89  per  cent,  of  the  dry. 
The  explanation  of  this  may  be  found  in  the  fact  that  in  the 
poor  concrete  the  mortar  was  "brash,"  and  the  concrete  did 
not  ram  well  with  a  dry  mortar,  while  the  rich  mortar  was 
"fuller"  and  more  plastic,  so  that  the  excess  of  water  was  not 
needed  to  make  a  compact  mass. 

426.  Turning  to  the  question  of  the  amount  of  mortar,  it  is 
plainly  shown  that  the  concrete  containing  forty  per  cent,  is 
but  little  better  than   that   containing  thirty-three   per   cent. 
This  is  in  line  with  what  has  been  said  elsewhere,  that  an  excess 
of  mortar,  as  well  as  a  deficiency,  may  be  an  actual  detriment 
to  the  strength  of  the  concrete.     In  this  case  the  thirty-three 
per  cent,  mortar  was  not  quite  sufficient  to  fill  the  voids  in 
the  stone,  and  forty  per  cent,  was  a  very  slight  excess. 

Some  interesting  conclusions  are  indicated  by  the  results  in 
the  line  marked  "ratios,"  near  the  bottom  of  the  table.  The 
ratios  of  the  strength  of  the  concrete  containing  thirty-three 
per  cent,  mortar  to  the  strength  of  that  containing  forty  per 
cent,  are  91.6  per  cent.,  98.5  per  cent,  and  102.6  per  cent.,  re- 
spectively, for  one-to-two,  one-to-three,  and  one-to-four  mor- 
tars. That  is,  with  a  rich  mortar  forty  per  cent,  may  be  used 
to  advantage,  but  if  the  mortar  is  of  poor  quality,  the  strength 
of  the  concrete  is  not  increased  by  an  excess  of  rnortar. 


CEMENT  AND  CONCRETE 


Finally,  as  to  the  strength  developed  under  different  con- 
ditions of  storage,  column  "  k  "  shows  that  for  these  cements  the 
highest  strengths  are  attained  by  immersing  the  concrete  in 
water.  In  comparison,  the  strength  developed  by  the  concrete 
covered  with  wet  burlap  is  84  per  cent. ;  in  cool  cellar,  82  per  cent. ; 
and  in  the  open  air  fully  exposed  to  the  weather,  81  per  cent. 

427.  The  results  given  in  Table  132  are  the  mean  crushing 
strengths  obtained  in  the  same  series  of  tests  as  described  above, 
so  arranged  as  to  bring  out  the  effect  of  the  richness  of  the 
mortar.  Although  several  brands  were  tested,  only  the  results 
obtained  with  a  single  brand  of  Portland,  namely,  Milieu's 
"Wayland,"  are  included  here,  since  the  series  was  not  com- 
pleted with  other  brands.  From  similar  tests  with  concretes 
containing  one-to-two  and  one-to-three  mortars  only,  it  was 
found  that  three  other  brands  of  Portland  gave  from  91  to  102 
per  cent,  of  the  strength  obtained  with  the  Wayland,  and  a 
brand  of  sand-cement  gave  66  per  cent. 


TABLE   132 

Compressive  Strength  of  Concrete.     Effect  of  Richness  of  Mortar 
MEAN  RESULTS,  FOUR  METHODS  or  STORAGE 


MORTAR,  PROPORTIONS  CEMENT  TO  SAND. 

VOLUME  MOR- 

TAR  \8 

CONSISTENCY 

PER  CENT.  OF 

OF 

1-1 

1-2                1-3 

1-4 

1-5 

VOLUME  OF 

CONCRETE. 

AGGREGATE. 

Crushing  Strength,  Lbs.  per  Sq.  In. 

( 

Moist  Earth    . 

4267 

2888 

2056 

1810 

1537 

33       \ 

Mason's     .  .  . 

4072 

2777 

2207 

1600 

1568 

I 

Quaking    .  .   . 

3764 

2847 

1723 

1767 

1441 

( 

Moist  Earth    . 

3966 

3404 

2179 

1671 

1559 

40       I 

Mason's    .  .  . 

4123 

2960 

2027 

1750 

146o 

I 

Quaking    .  .  . 

3256 

3168 

2016 

1670 

1400 

Mean 

3908 

3007 

2035 

1711 

1495 

Proportional    . 

100 

77 

52 

44 

38 

NOTES:  — One  brand  Portland  cement. 

Aggregate,  Portage  sandstone,  broken  to  pass  two-inch  ring. 
Age  of  cubes  about  twenty  months. 
Each  result,  mean  of  four  cubes. 


CONCRETE 


297 


Each  result  in  the  table  is  the  mean  of  four  cubes,  each 
stored  in  a  different  manner.  Tests  with  four  brands  (Table 
131)  where  the  concretes  were  made  with  one-to-two,  one-to- 
three  and  one-to-four  mortars,  indicated  that  the  percentages  of 
the  mean  strength  developed  in  the  several  methods  of  storage 
were  as  follows:  If  stored  in  water,  the  cubes  developed  115  per 
cent,  of  the  mean  result;  covered  with  burlap  kept  wet,  the 
cubes  developed  97  per  cent. ;  stored  in  a  cool  cellar,  95  per 
cent.;  and  fully  exposed  to  weather,  93  per  cent,  of  the  mean 
strength. 

The  mean  results  given  at  the  bottom  of  the  table  represent 
each  a  mean  of  twenty-four  cubes  made  with  two  different 
amounts  of  mortar,  three  degrees  of  consistency,  and  four 
methods  of  storage.  By  applying  the  percentages  given  above 
the  probable  corresponding  result  for  any  set  of  conditions 
may  be  obtained.  The  last  line  of  the  table  shows  the  propor- 
tions that  the  strength  of  the  concretes  made  with  poorer  mor- 
tars, bear  to  the  strength  obtained  with  one-to-one  mortar. 

428.  Table  133  gives  the  results  of  a  series  of  tests  made  by 
J.  W.  Sussex  at  the  University  of  Illinois.1  The  materials  used 
were  ''Chicago  AA  Portland  cement,  sand  containing  a  small 

TABLE  133 

Compresaive  Strength    of   Concrete.       Relative    Strength    of    Dry, 
Medium,  and  Wet  Mixtures 


TENSILE  STRENGTH,  POUNDS  PER 

SQUARE  INCH,  AT  AGE  OP 

PROPOR- 

CONSISTENCY. 

TAMPING. 

TIONAL  VALUK 

AT  3  Mo*. 

7  days. 

1  month. 

3  months. 

Dry   .     . 

Light 

1200 

1750 

2500 

82 

Medium           .     . 

u 

2290 

221)0 

2150 

71 

Wet  .     . 

tt 

1040 

2230 

3040 

100 

Dry   .     . 

Hard 

1340 

1960 

2000 

86 

Medium           .     . 

u 

1330 

2565 

2580 

85 

NOTES:  —  Concrete  composition: 

Cement,  Portland,  one  volume. 

Sand,  containing  some  fine  gravel,  three  volumes. 

Six  volumes  broken  limestone  passing  one-inch  mesh. 
Specimens,  six-inch  cubes. 
Results  by  J.  W.  Sussex,  Univ.  of  111. 


Technograph,  1902-03. 


298  CEMENT  AND  CONCRETE 

percentage  of  fine  gravel,  and  crushed  limestone  which  would 
pass  through  a  sieve  with  one-inch  mesh."  The  proportions 
were  three  parts  sand  and  six  of  broken  stone  to  one  volume  of 
loose  cement.  The  cubes  were  six  inches  on  a  side.  The 
treatment  during  storage  is  not  stated.  The  consistency  of 
the  concrete  was  as  follows:  "Dry,"  water  6.0  per  cent.,  as 
moist  as  damp  earth,  no  free  water  flushed  to  surface  in  ram- 
ming. "Medium/'  7.8  per  cent,  water;  water  flushed  to  surface 
and  concrete  quaked  only  after  being  well  rammed.  "Wet/' 
water  9.4  per  cent.,  concrete  quaked  in  handling  and  could  be 
tamped  but  lightly. 

Each  result  in  the  table  is  the  mean  of  three  cubes.  The 
concrete  was  tamped  in  layers  about  one  inch  thick  with  a 
rammer  weighing  11^  pounds  and  dropped  six  inches.  Ten 
blows  of  the  rammer  constituted  "light"  tamping  and  twenty 
blows  "hard"  tamping.  The  results  show  that  the  "medium" 
concrete  gains  its  strength  more  rapidly  than  the  "wet,"  but 
that  at  one  month  the  "wet"  concrete  has  a  higher  strength 
than  the  dry,  and  that  at  three  months  the  wet  surpasses  in 
strength  both  the  dry  and  the  medium. 

ART.  54.     CONCRETES  WITH  VARIOUS  KINDS  AND  SIZES  OF 
AGGREGATES 

429.  It  has  already  been  stated  that  the  character  of  the 
aggregates  is  second  only  to  the  quality  of  the  mortar  in  its 
effect  on  the  strength  of  concrete.  The  materials  available  for 
aggregate  in  different  localities  are  so  varied  that  only  a  general 
idea  of  their  relative  values  may  be  obtained  from  a  limited 
number  of  tests. 

The  results  given  in  Table  134  are  from  tests  made  at  the 
Watertown  Arsenal/  and  show  the  compressive  strengths  of 
concretes  made  with  broken  trap  and  gravel  of  different  sizes. 
The  concretes  are  all  very  rich,  and  the  strengths  correspond- 
ingly high,  although  the  oldest  specimens  have  hardened  less 
than  three  months.  The  results  are  somewhat  irregular,  and 
the  conclusion  to  be  drawn  concerning  the  best  size  for  the 
aggregate  is  not  very  clearly  brought  out.  The  one-inch  trap 
gives  uniformly  good  results,  as  do  the  mixtures  of  two  or 


1  "Tests  of  Metals/'  1898. 


CONCRETE 


299 


more  sizes.  The  trap  rock  gives  a  higher  result  than  the  gravel, 
the  mortar  being  sufficient  to  fill  the  voids  in  the  trap,  and  in 
excess  for  the  gravel. 

TABLE   134 

Compressive  Strengths  of  Rich  Concretes  at  Different  Ages 
TESTS  OF  TWELVE— INCH  CTBES 


WT.  PKK 

CU.FT.OF 

C'oMPKKMHivn  STRENGTH,  POUNDS  I»KR 

('ONTKKTK 

SQUARE  INCH,  AT  AGE,  DAYS, 

CHARACTER  OF  AGGREGATE. 

WHKN 

Mo.  OLD, 
IN  LBS. 

7-8 

19-23 

29-34 

61-76 

Trap  \" 

148  6 

1391 

2220 

2800 

5021 

y 

148  5 

1900 

2760 

3200 

150.8 

3800 

4254 

4917 

5272 

\\" 

150  2 

3180 

4000 

4662 

2583 

2J"  

160.2 

2400 

4143 

4140 

4523 

i"-i,  2r-2.    .    .   . 

158.4 

2800 

3786 

4340 

45441 

*"-!,  1"-1,  2}"-l 

150.8 

2800 

4156 

4800 

5542 

Mean  results,  trap  rock  alone 

2553 

3619 

4110 

4581 

Pebbles  I"  . 

148.2 

1208 

2600 

2002 

3870 

"       H"      

161.0 

2276 

3186 

3817 

4018 

"       f'-l,  lJ"-2  .     .     . 

150.3 

1004 

3023 

3800 

345M) 

"    t"-i,  §•'-!,  ij"-i 

147.8 

1480 

2676 

3000 

3800 

Mean,  pebbles  alone  . 

1764 

2871 

3402 

3794 

NOTES:  —Tests  made  at  Watertown  Arsenal,  "Tests  of  Metals,"  1898. 

All  concretes  composed  of  one  cubic  foot  of  Alpha  Portland  cement, 
weight  06i  to  106  Ibs.  per  cu.  ft.,  one  cu.  ft.  of  bank  sand, 
weight  93^  to  104  Ibs.  per  cu.  ft.,  and  3  cu.  ft.  of  aggregate, 
weighing  from  93  to  105  Ibs.  per  cu.  ft. 

The  size  of  aggregate  indicated  gives  the  larger  of  the  two  screens 
used  in  separating  it  into  different  sizes;  thus,  "  f  inch" 
means  passing  f  inch  mesh  and  retained  on  \  inch  mesh. 

The  compressive  strength  of  twelve  inch  cubes  of  one-to-one  mor- 
tar alone  was  3,833  Ibs.  per  sq.  in.  at  seven  days,  and  4,800 
Ibs.  per  sq.  in.  at  seventy-five  days. 

430.    In   1896-97   Mr.   A.  W.   Dow2  prepared   a   number  of 
twelve-inch  cubes  of   concrete  for  the   Engineer  Commissioner 


1  Not  fractured. 

2  Report  Operations,  Engineer  Department,  District  of  Columbia,  1897. 
Also  Baker's  "Masonry  Construction,"  p.  112  r. 


300 


CEMENT  AND  CONCRETE 


of  the  District  of  Columbia.  These  cubes  are  of  interest  as 
showing  the  strength  of  natural  cement  concrete  as  well  as 
Portland,  and  the  results  are  abstracted  in  Table  135. 

TABLE    135 

Compressive  Strength  of  Concrete 

TESTS  OF  TWELVE-INCH    CUBES    FOR  THE    ENGINEER  COMMISSIONER   OF   THE 
DISTRICT  OF  COLUMBIA 


REF. 

COMPOSITION  OF  CONCRETES. 

PER 
CENT. 

VOIDS  IN 
AGGRE- 
GATE. 

CRUSHING 
STRENGTH,    LBS. 
PER  SQVAKE 
INCH  AT  ONE 
YEAR. 

Cement. 

Sand. 

Broken  Stone. 

Gravel. 

Port- 
land. 

Natural. 

Coarse. 

Average. 

Average. 

Small. 

1 
2 
3 
4 
5 
6 

1 
1 
1 
1 
1 
1 

2 
2 
2 
2 
2 
2 

6 

45.3 
45.3 
30.5 
29.3 
35.5 
36.7 

1850 
3060 
2700 
2820 
2750 
2840 

829 
915 
800 
763 
841 
915 

6 
61 

'    3'   ' 
4 

0 

3 
2 

NOTES:  —  Materials: 

Cement,    Portland,    "Atlas"    (American),    104   Ibs.    per    cu.  ft.;  Natural, 

"Round  Top,"  70  Ibs.  per  cu.  ft. 
Sand,  15  per  cent,  retained   on   No.  8  mesh,  75  per  cent,  between  8  and 

40  mesh,   10  per  cent,  passing  40  mesh.     Sand  was  used  damp,  and 

weighed  in  that  condition  90  Ibs.  per  cu.  ft. 

Stone,  Bluestone,  "Average,"  93  percent,    between    ^  inch   and  2   inches. 
"Coarse,"  89  per  cent,  between  1|  inches  and  2$  inches. 
Gravel,  "Average,"  90  per  cent,  between  £  inch  and  1£  inches. 

"Small,"   90   per   cent,    between   £  inch   and   f  inch. 
Granolithic,  92  per  cent,  between  -^  inch  and  £  inch. 
Mixing,  thorough  by  experienced  man. 

Tamping,  light,  in  4  inch  layers,  just  sufficient  to  bring  mortar  to  surface. 
Storage,  cubes  thoroughly  wet  twice  a  day. 
Age  of  specimens  when  broken,  one  year. 

The  concretes  all  contained  two  parts  sand  and  six  parts 
aggregate  to  one  cement,  but  the  character  of  the  aggregate 
varied  as  shown.  The  natural  cement  concrete  gave  from  one- 
quarter  to  one-third  the  strength  of  the  Portland  concrete. 
The  best  result  seems  to  be  given  by  the  average  size  broken 
stone,  which  was  in  reality  a  mixture  of  various  sizes,  ninety- 


Mixture  of  one  part  granolithic  size  to  one  of  concrete  stone. 


CONCRETE 


301 


three  per  cent,  of  it  being  retained  on  a  one-third  inch  mesh 
and  passing  a  two-inch  mesh.  The  mortar  was  probably  in- 
sufficient to  fill  the  voids  in  the  stone  for  the  first  three  cubes 
in  the  table,  and  under  these  conditions  the  gravel,  with  its 
smaller  percentage  of  voids,  makes  a  good  showing.  This  illus- 
trates what  we  have  already  said,  that  the  relative  value  of 
broken  stone  and  gravel  for  aggregate  depends  upon  the  pro- 
portion of  mortar  used. 

TABLE   136 

Compressive  Strength  of  Concrete.     Portland  Cement 
TESTS  OF  SIX-INCH  CUBES  OF  VARIOUS  MIXTURES 


UKFKHENCE. 

PARTS  BY  VOLUME  TO 
ONE  CEMENT. 

CRUSHING  STRENGTH,  POUNDS  PER  SQUARE 
INCH,  AT  AGE  OF, 

Sand. 

Gravel. 

Broken 
Stone. 

7  days. 

30  days. 

90  days. 

1 

0 

0 

0 

3412 

5318 

6140 

2 

0 

31 

0 

1077 

1908 

2517 

3 
4 

1 
2 

2 
2 

i* 

1430 
420 

2215 
2117* 

2903 
1324 

5 

2 

3 

4 

640 

1199 

1290 

6 

7 

l\ 

5 
0 

0 
5 

566 
739 

1385 
2033 

1609 
1783 

8 

2£ 

2£ 

21 

792 

1482 

2014 

9 

3 

o 

o 

767 

1345 

1409 

10 

3 

3 

4 

714 

'  1028 

1818 

Means,  Actual 
Means,  Per  Cent 

1056 
46 

2003 
88 

2284 
100 

NOTE  :  —  Results  of  Messrs.  Ketchum  and  Honens. 

431.  The  results  in  Table  136  were  obtained  by  Messrs.  R. 
B.  Ketchum  and  F.  W.  Honens  at  the  laboratory  of  the  Uni- 
versity of  Illinois,3  and  illustrate  the  rate  of  gain  in  strength 
of  several  mixtures.  The  cement  used  was  Baylor's  Portland, 
fine  and  of  good  quality.  The  sand  and  gravel  were  composed 
principally  of  silica,  with  10  to  30  per  cent,  of  limestone.  About 
60  per  cent,  of  the  sand  passed  a  " number  thirty"  sieve.  The 
unscreened  gravel  had  about  42  per  cent,  caught  on  a  "  num- 
ber five"  sieve  and  eighteen  per  cent,  of  it  passed  a  "number 


1  Unscreened. 

2  Result  irregular. 

3  Technograph,  1897-98. 


302  CEMENT  AND  CONCRETE 

thirty."  Except  in  one  mixture,  however,  the  gravel  and 
broken  stone  were  screened,  and  only  that  portion  passing  a 
two-inch  ring  and  retained  on  a  " number  five"  sieve  was  used. 
The  stone  was  a  magnesian  limestone. 

The  concrete  was  mixed  dry,  so  that  considerable  tamping 
was  required  to  bring  water  to  the  surface.  The  cubes  were 
first  kept  under  a  damp  cloth  for  one  day,  immersed  six  days, 
and  then  stored  in  air  in  a  room  until  broken.  In  crushing; 
"the  direction  of  the  force  applied  was  parallel  to  the  tamped 
surface." 

432.  Each  result  in  the  table  is  the  mean  of  six  specimens. 
Comparing  number  2  with  number  9  indicates  that  the  strength 
obtained  with  one  part  cement  to  three  parts  unscreened  gravel 
is  much  higher  than  with  mortar  of  one  part  cement  to  three 
parts  sand.     Comparing  9  and   10  indicates  that  seven  parts 
gravel  and  stone  may  be  mixed  with  one-to-three  mortar  and 
give  higher  strength  than  the  mortar  alone.     A  comparison  of 
6,  7,  and  8  shows  that  in  case  there  is  sufficient  mortar  to  fill 
the  voids  in  the  aggregate,  angular  fragments  give  a  somewhat 
higher  strength  than  rounded  ones,  but  that  a  mixture  of  broken 
stone  and  gravel  is  better  than  either  alone.     One  of  the  most 
important  points  brought  out  by  the  tests  is  that  the  strength 
at  seven  days  is  46  per  cent.,  and  at  thirty  days  is  88  per  cent., 
of  the  strength  attained  at  three  months. 

ART.  55.     CINDER  CONCRETE,  ETC. 

433.  For  such  purposes  as  floors  for  buildings,  cinders  are 
used  in  concrete  to  a  considerable  extent  on  account  of  their 
light  weight.     Cinder  concrete  weighs  only  from  two-thirds  to 
three-fourths    as    much    as    broken    stone    or    gravel    concrete. 
The  strength,  however,  is  correspondingly  less,  and  whether  for 
a  given  strength  a  floor  may  be  made  lighter  by  the  use  of 
cinders  will  depend  upon  the  conditions  of  use  and  the  charac- 
ter of  the  reinforcement. 

Table  137  gives  the  results  of  the  tests  of  eight-inch  cylinders, 
fifteen  inches  high,  made  by  Mr.  George  Hill.1  In  these  cylin- 
ders, cinders,  broken  stone,  and  gravel  were  used  as  aggregates. 
The  character  of  the  materials  is  shown  in  the  foot-note  of  the 


Trans.  Am.  Soc.  C.  E.,  Vol.  xxxix,  p.  632, 


CINDER  CONCRETE 


303 


table.  As  the  specimens  were  but  one  month  old  when  tested, 
the  results  are  low,  but  since  in  the  construction  of  floor  arches 
the  centers  are  usually  removed  in  less  than  one  month,  the 
strength  developed  in  a  short  time  has  a  special  interest. 

TABLE   137 

Compressive  Strength  of  Concrete   about   One  Month  Old 
TESTS  OF  CYLINDERS,  EIGHT  INCHES  DIAMETER,   FIFTEEN  INCHES  HIGH 


PROPORTIONS  BY  VOLUMK. 

AGE, 

COMPRESSIVE  STRENGTH, 
LBS.  PER  SQ    IN. 

AGGREGATE. 

Cement. 

Sand. 

Aggregate. 

Days. 

American 
Portland 
Cement. 

Slag 
Cement. 

Cinders. 

.3 

6 

33 

246 

« 

3 

6 

18 

292 

« 

2 

5 

33 

305 

it 

2 

5 

33 

4(J4 

it 

2 

5 

32 

490 

K 

2.4 

6 

32 

590 

i( 

1.7 

4.2 

30 

342 

(t 

1.8 

4 

30 

330 

(I 

1.8 

4 

31 

766 

(( 

1.8 

4 

31 

765 

Stone. 

3 

6 

30 

398 

" 

2.4 

4.1 

30 

503 

u 

2.4 

4 

33 

645 

u 

2.4 

4 

30 

730 

Gravel. 

3 

6 

30 

oi7 

618 

« 

1 

2.4 

4.8 

30 

650 

u 

1 

2 

7 

25 

880 

(1 

1 

1.8 

6.5 

31 

730 

Stone  and  gravel,    ) 
graded    .  .  .  .   \ 

1 

2 

10 

30 

625 

... 

NOTES:  — 

Cement,  American  Portland,  tensile  strength  624  Ibs.  per  sq.  in.,  neat,  seven 
days. 

Slag  cement,  a  little  less  than  400  Ibs.  per  sq.  in.,  neat,  seven  days. 
Sand,  clean,  sharp,  bank  sand  of  mixed  sizes,  from  moderately  fine  up  to 

some  pebbles  size  of  bean. 
Cinders,  ordinary  steam,  dust  to  £  inch  size. 
Stone,  broken  trap,  nearly  uniform  size  passing  l\  inch  ring. 
Gravel,  clean,  washed,  \  in.  to  1^  in. 
Abstract  of  tests  by  Mr.  George  Hill,  M.  Am.  Soc.  C.  E.,  Vol.  xxxix,  p.  632. 

It  is  evident  that  cinder  concrete  should  not  be  loaded  very 
heavily  within  a  month  after  made.  The  gravel  gives  a  better 
result  than  broken  stone. 


304 


CEMENT  AND  CONCRETE 


434.  In  Table  138  are  given  the  results  of  some  tests  of 
twelve-inch  cubes  of  cinder  concrete  made  at  the  Watertown 
Arsenal  for  the  Eastern  Expanded  Metal  Companies.  Steam 
cinders  were  used,  practically  as  they  came  from  the  furnace, 
only  the  larger  clinkers  being  broken.  Two  proportions  were 
used  and  the  specimens  were  broken  at  one  month  and  three 
months.  It  is  seen  that  the  one-one-three  mixture  is  about 
twice  as  strong  as  the  one-two-five  with  all  brands.  The  varia- 
tions between  the  several  brands  are  also  very  great. 

TABLE   138 

Crushing  Strength   of  Cinder  Concrete.     Portland  Cement 
TESTS  OF  TWELVE-INCH  CUBES  AT  WATERTOWN  ARSENAL 


BRAND 

OF 

CEMENT. 

STRENGTH,  POUNDS  PER  SQUARE  INCH. 

Mixture  A,  1-1-3. 

Mixture  B,  1-2-5. 

Age  of  Specimens. 

Age  of  Specimens. 

1  month. 

3  months. 

1  month. 

3  months. 

A 
B 
C 
D 

2329 
1602 
1438 
1032 

2834 
2414 
1890 
1393 

940 
696 
744 
471 

1600 
1223 
880 
685 

NOTES:  — 

Concretes  mixed  rather  dry,  10  to  12J  pounds  of  water  per  cubic  foot  of 

concrete. 

Mixture  "A,"  one  part  cement,  one  part  sand,  three  parts  cinders. 
Mixture  "B,"  one  part  cement,  two  parts  sand,  five  parts  cinders. 
Weight  of  concrete,  104  to  116  pounds  per  cubic  foot. 
Tests   for  Eastern  Expanded  Metal  Companies.     Data   from    "Tests   of 
Metals/'  1898. 

435.  Table  139  gives  the  results  of  other  tests  in  the  same 
series,  using  a  single  brand  of  cement  and  five  mixtures,  the 
richest  containing  three  parts  cinders  and  one  part  sand  to  one 
volume  cement,  and  the  poorest  six  parts  cinders  and  three 
parts  sand  to  one  cement.  The  weight  per  cubic  foot  of  the 
several  concretes  is  also  given. 

Tests  of  cinder  concrete  prisms  made  by  the  late  Prof.  J.  B. 
Johnson  at  Washington  University  *  indicated  that  the  mixture 


Materials  of  Construction,"  p.  628. 


CONCRETE   WITH   CLAY 


305 


containing  one  part  sand  and  three  parts  cinders  to  one  volume 
cement  gave  the  highest  strength,  or  about  twelve  hundred 
pounds  per  square  inch,  at  one  month.  The  same  mixture  gave 
the  highest  values  for  the  ratios  of  strength  to  cost,  and  of 
strength  to  weight  per  cubic  foot. 

TABLE    139 

Crushing  Strength  of  Cinder  Concrete.     Various  Proportions  with 

Germaiiia    Portland    Cement 
TESTS  OF  TWELVE-INCH  CUBES  AT  WATERTOWN  ARSENAL 


PROPORTIONS  IN  CONCRETE. 

WEIGHT  PER 
Cu.  FT.  AT  98 
TO  102 
DAYS,  POUNDS. 

CRUSHING  STRENGTH, 
POUNDS  PER  SQUARE  INCH, 
AT  AGE, 

Cement. 

Sand. 

Cinders. 

29  to  39  days. 

98  to  102  days. 

1 
1 
1 
1 
1 

1 
2 
2 
2 
3 

3 
3 
4 
5 
6 

110.4 
112.8 
107.9 
105.3 
103.5 

1406 
1008 
904 
760 
529 

2001 
1634 
1325 
1084 
788 

NOTE:  — Tests  for  Eastern  Expanded  Metal  Companies,  "Tests  of  Metals," 
1898. 

436.  Clay  in  Concrete.  —  The  effect  of  clay  on  the  tensile 
strength  of  mortars  has  already  been  shown  (Art.  49).  Aggre- 
gates available  for  concrete  frequently  contain  a  certain  amount 
of  clay,  and  the  question  arises  whether  such  aggregate  must 
be  washed,  or  whether  certain  small  percentages  may  be  per- 
mitted in  the  concrete,  using,  perhaps,  a  trifle  richer  mortar. 
The  results  in  Table  140  were  made  to  determine  the. effect  of 
clay  on  the  crushing  strength  of  concrete.1 

The  test  specimens  were  six-inch  cubes,  and  were  broken 
when  one  week  to  twelve  weeks  old  in  an  Olsen  machine.  The 
proportions  were  two  parts  sand  and  six  parts  gravel  by  weight 
to  one  of  Portland  cement,  or  two  parts  sand  and  four  parts 
gravel  by  weight  to  one  of  natural  cement.  The  clay  is  ap- 
parently expressed  as  the  per  cent,  of  total  aggregates.  It  is 
seen  that  while  six  or  twelve  per  cent,  clay  retards  the  harden- 
ing of  both  Portland  and  natural  cement  concrete,  the  strength 
of  the  Portland  concrete  after  four  weeks  is  increased  by  six  per 


1  Tests  by  Messrs.  J.  J   Richey  arid  B.  H.  Prater,  Technograph,  1902-03. 


306 


CEMENT  AND  CONCRETE 


cent,  clay,  while  at  the  same  age  the  strength  of  the  natural 
cement  concrete  is  not  greatly  affected.  The  ramming  of  con- 
crete is  facilitated  by  the  presence  of  a  small  amount  of  clay, 
but  larger  amounts  may  render  the  mass  sticky  and  difficult 
to  ram. 

TABLE    140 

Effect  of  Clay  on  Crushing  Strength  of  Concrete 
SIX-INCH  CUBES 


CEMENT. 

PROPORTIONS  BY 
WEIGHT,  No.  PARTS 
TO  ONE  CEMENT. 

AGE  OF  CUBES 

WHEN 

CRUSHING  STRENGTH,  POUNDS  PER  SQ. 
IN.;  CLAY  AS  PER  CENT.  OF  CONCRETE, 

Sand. 

Gravel. 

BROKEN. 

0 

6 

12 

Port. 

2 

6 

1  week 

1030 

1001 

692 

ti 

2 

6 

4  weeks 

1398 

1525 

1287 

u 

2 

6 

12      " 

2110 

2760 

1865 

Nat. 

2 

4 

1  week 

208 

131 

81 

u 

2 

4 

4  weeks 

428 

364 

283 

u 

2 

4 

12      " 

786 

722 

480 

ART.  56.     THE  MODULUS  OF  ELASTICITY  OF  CEMENT  MORTAR 

AND  CONCRETE 

437.  With  the  increasing  use  of  concrete  and  steel  in  com- 
bination, the  modulus  of  elasticity  of  cement  mortar  and  con- 
crete assumes  a  new  importance,  since  the  ratio  of  the  stresses 
in  the  two  materials  depends  upon  the  relative  moduli  of  elas- 
ticity.    Some  of  the  earlier  determinations  of  the  modulus  of 
mortar  gave  very  high  values.     This  may  have  been  due  to  the 
use  of  richer  mixtures,  and  the  exercise  of  greater  care  in  the 
manipulation,  than  are  employed  in  actual  construction,  and 
also  to  the  fact  that  the  determinations  were  based  upon  the 
deformations   resulting   from   the   application   of   very   limited 
loads. 

It  is  now  considered  that  the  ratio  of  stress  to  strain  is  not 
constant,  even  for  moderate  loads,  but  that  the  modulus  of 
elasticity  decreases  with  increasing  stress,  and  this  fact  is  brought 
out  in  the  following  tables.  The  tests  cited  bring  out  a  wide 
range  of  values  for  concretes  and  mortars  made  from  a  variety 
of  sand  and  aggregate  and  of  various  compositions  and  ages. 

438.  Modulus  of  Elasticity  of  Natural  and  Portland   Cement 
Mortars.  —  Table  141  gives  the  modulus  of  elasticity  of  mortars 
as  determined  by  tests  of  twelve-inch  cubes  at  the  Watertown 


MODULUS  OF  ELASTICITY 


307 


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308 


CEMENT  AND  CONCRETE 


Arsenal.1  These  specimens  were  a  portion  of  those  prepared 
by  Mr.  Rafter,  the  compressiva  strength  being  given  in  Table 
129.  As  each  value  is  the  result  of  but  one  determination,  the 
results  are  not  as  regular  as  might  be  desired.  In  general  the 
strength  and  the  modulus  decrease  together  as  the  amount  of 
water  used  in  mixing  is  increased.  The  modulus  also  decreases 
with  the  strength  as  the  proportion  of  sand  increases. 

439.  Modulus  of  Concretes  One  Month  to  Six  Months  Old.  - 
In  the  compressive  tests  of  twelve-inch  concrete  cubes  made 
for  Mr.  George  A.  Kimball  and  abstracted  in  Table  130,  many 
of  the  specimens  were  also  gaged  for  compression  under  load  to 
determine  the  modulus  of  elasticity,  and  a  part  of  the  results 
are  presented  in  Table  142. 

TABLE    142 
Modulus  of  Elasticity  of  Concrete 

TESTS  MADE  ON  TWELVE-INCH  CUBES  OF  PORTLAND  CEMENT  CONCRETE  AT 
WATERTOWN  ARSENAL  FOR  BOSTON  ELEVATED  RAILROAD 


AGE 
OP  CUBES 
WHEN 
CRUSHED. 

CONCRETE  1-2-4. 

CONCRETE  1-3-6. 

CONCRETE  1-6-12. 

Modulus  of  Elasticity  in  Thousands,  between  Loads, 
in  Pounds  per  Square  Inch,  of 

100-600 

100-1000 

1000-200:) 

100-600 

100-1000 

1000-2000 

100-600 

100-1000 

7  days 
1  month 
3  months 
6  months 

2592C 
2662c 
3670 
3646 

2053c 
2444c 
3170 
3567 

1351a 

1462c 
2157 
2581 

1869c 
2438 
2976 
3608 

15296 
2135 
2656 
3503 

1210a 
1805 
1868 

1376 
1642 
1820 

1363 
1522 

are  means  of  five  or  more  tests  of  one  brand, 
are  means  of  five  or  more  tests  on  each  of 

are  means  of  five  or  more  tests  on  each  of 


NOTES:  —  Results  marked  "a! 
Results  marked  "b 

two  brands. 
Results  marked  "c 

three  brands. 
Results  not  marked  are  means  of  five  or  more  tests  on  each  of 

four  brands,  two  American,  two  German. 
For  compressive  strengths  of  similar  cubes,  see  Table  130. 

It  is  seen  that  the  modulus  increases  with  the  age  and  rich- 
ness of  the  specimens,  and  decreases  as  the  load  increases.  For 
one-two-four  concrete  the  modulus  at  one  month,  for  loads 
between  a  hundred  and  a  thousand  pounds,  is  about  two  and 


1  "Tests  of  Metals,"  1899. 


r 

MODULUS  OF  ELASTICITY  309 

one-half  million,  and  for  six  months,  three  and  a  half  million. 
The  corresponding  values  for  the  one-three-six  concrete  are  two 
million  and  three  and  one-half  million.  When  the  ultimate 
strength  is  approached,  the  modulus  of  elasticity  decreases 
rapidly,  and  between  loads  of  one  thousand  and  two  thousand 
pounds  per  square  inch,  the  richest  concrete  gives  only  about 
one  and  one-half  and  two  and  one-half  million  at  one  month 
and  six  months,  respectively. 

440.  Modulus  of  Concrete  Dependent  on  Richness  of  Mortar. 
-  The  results  in  Table  143  are  abstracted  from  the  extensive 

tests  made  at  the  Watertown  Arsenal  for  the  State  Engineer 
of  New  York.  Although  several  brands  were  testetl,  the  results 
in  the  table  are  from  one  brand  only,  namely,  "Waylaml" 
Portland.  These  cubes  were  all  stored  in  the  same  manner, 
namely,  in  water  three  to  four  months,  and  then  buried  in  damp 
sand  until  broken  at  the  age  of  twenty  months.  The  mean 
ultimate  strengths  of  similar  cubes  stored  according  to  four 
methods  are  given  in  Table  132. 

Since  in  all  of  these  mixtures  the  quantity  of  mortar  was  a 
given  percentage,  either  thirty-three  or  forty,  of  the  volume  of 
aggregate,  the  effect  of  the  richness  of  the  mortar  may  be  studied. 
While  the  proportional  strengths  of  the  concretes  made  with 
mortars  containing  from  one  to  five  parts  sand  are  100,  77,  52, 
.44,  and  38,  the  corresponding  proportional  moduli  of  elasticity 
are  100,  92,  77,  60,  and  55,  the  modulus  decreasing  less  rapidly 
than  the  strength,  with  the  addition  of  sand. 

441.  Gravel  and  Trap  Aggregates.  —  Table   144  gives  the  re- 
sults of  the  determinations  of  the  modulus  of  elasticity  of  con- 
crete specimens  made  and  tested  at  the  Watertown  Arsenal,1 
the  strength  of  which  was  given  in  Table  134.     As  these  are  all 
rich   concretes,   the  moduli  and   the  strengths   are   high.     The 
values  of  the  modulus  for  the  gravel  concretes  are  about  70 
per  cent,  of  those  for  the  trap,  but  the  strengths  of  the  gravel 
concretes  are  in  general  about  80  per  cent,  of  those  obtained 
with  concretes  having  trap  aggregate.     In  a  general  way,  how- 
ever, the  modulus  and  strength  vary  together. 

442.  Modulus   of   Cinder   Concrete.  —  The  modulus  of  elas- 
ticity of    cinder    concrete    prepared  for  the  Eastern  Expanded 


'Tests  of  Metals,"  1898. 


310 


CEMENT  AND  CONCRETE 


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O  '  i—  i  '  O 


T-H  (N  O  Oi  O  CO 
t-  CO  O  OO  O  i—i 
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O  CO    i—  1  l-~  C 

(M  CO    CO  -^  i 


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TfH  CD  O 


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CO  CM      i—  I  CD 
- 


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O  O 


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CO  l>-     t^  rH 
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PROPORTION 
CEMENT  TO 
SAND  IN  MORTAR. 


nsistency 
Concrete. 


axvoaHooy  awmoA 

£0    -XN33  H3J 

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MODULUS  OF  ELASTICITY 


311 


TABLE    144 

Modulus   of  Elasticity  of  Rich   Concretes   with   Gravel  and 
Trap  as  Aggregates 

TESTS  OF  TWELVE-INCH  CUBES  AT  WATERTOWN  ARSEXAL.     1-1-3,  ALPHA 

CEMENT 


CHARACTER  OF  AGGREGATE. 

MODULUS  OF  ELASTICITY  IN  THOUSANDS,  BE- 
TWEEN LOADS  OF  100  AND  1,000 
POUNDS  PER  SQUARE  INCH,  AT  AGE,  DAYS, 

7-8 

19-23 

29-34 

61-76 

Trap  \ 

1875 
3214 

4091 
4500 
3214 
5000 
3401 

2500 
2808 
6429 
5025 
5<J25 
4500 
4500 

3750 
5025 
5(525 
5000 
4500 
7500 
5025 

3750 

'  5025  ' 
4091 
7">00 
5025 
7500 

1 

1                                 . 

2 

-1,  2y-2     .... 
-1,  1"-1,  2J"-1    .     . 

Mean  Results,  trap  rock  aloue 

3022 

4507 

5375 

5082 

Pebbles  f  "  

1800 
3750 

2812 
1800 

3750 
4091 
3461 
3214 

3461 
3750 
4091 
3461 

3214 
3000 
4500 
3214 

"      1$"  

"        f"-l,  lJ"-2       .     .     . 
"       I"-1*  I"-1*  li"-1     • 

Mean  Results,  pebbles  alone 

2540 

3629 

3091 

3482 

NOTES:  — 

Tests  at  Watertown  Arsenal,  "Tests  of  Metals,"  1898. 

For  crushing  strength  of  these  concretes,  see  Table  134. 

The  modulus  of  elasticity  of  twelve-inch  mortar  cubes,  one  volume  cement 
to  one  volume  sand,  was,  for  loads  between  five  hundred  and  one  thou- 
sand pounds  per  square  inch,  3,401,000  at  seven  days  and  5,000,000  at 
seventy-five  days. 

Metal  Companies  is  given  in  Table  145.  The  results  are  seen 
to  be  low,  as  is  the  crushing  strength.  The  permanent  set  in 
five-inch  gaged  length  for  a  load  of  six  hundred  pounds  per 
square  inch  is  also  shown  in  the  table. 


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CEMENT  AND  CONCRETE 


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1 

CHAPTER    XVII 

THE  TRANSVERSE  STRENGTH  AND  OTHER  PROPERTIES  OF 
MORTAR  AND  CONCRETE 

ART.  57.     TRANSVERSE  STRENGTH 
443.  TENSILE,  TRANSVERSE  AND  COMPRESSIVE  STRENGTHS 

OF  MORTAR  COMPARED.  —  The  tests  given  in  Tables  146  and 
147  were  designed  to  compare  the  strengths  of  cement  mortars 
in  tension,  bending  and  compression,  and  to  show  the  relative 
effect  on  the  three  kinds  of  strength  of  certain  variations  in 
manipulation. 

The  tensile  specimens  were  briquets  of  the  ordinary  form, 
made  in  brass  molds.  The  transverse  and  compressive  speci- 
mens were  made  in  wooden  molds,  the  bars  for  transverse  tests 
being  two  by  two  by  eight  inches  and  molded  horizontally, 
while  the  specimens  for  compressive  tests  were  two-inch  cubes. 
Specimens  of  the  three  forms  were  made  from  the  same  batch 
of  mortar  to  obviate,  as  far  as  possible,  variations  due  to  differ- 
ence in  gaging.  Two  cubes,  two  briquets  and  one  bar  were 
usually  made  from  one  gaging  of  mortar. 

The  briquets  were  broken  in  the  usual  manner  on  a  Riehle 
cement  testing  machine.  The  bars  were  broken  on  a  home- 
made lever  machine.  Two  fixed  knife  edges  were  placed  five 
and  one-third  inches  apart,  and  the  breaking  stress  was  applied 
through  a  third  knife  edge  at  mid-span.  The  lengths  of  the 
lever  arms  of  the  testing  machine  were  in  the  ratio  of  one  to 
twenty-five,  and  water  was  allowed  to  run  gently  into  a  vessel 
at  the  end  of  the  longer  arm.  The  span  of  five  and  one-third 
inches  was  chosen  because  at  this  length  the  modulus  of  rup- 
ture, for  a  two  inch  square  specimen,  has  the  same  numerical 
value  as  the  center  load  applied. 

The  cubes  were  crushed  in  a  crude  machine,  improvised  for 
the  purpose,  consisting  of  two  iron  plates,  two  hydraulic  jacks, 
with  hydraulic  weighing  gage  and  proper  framework.  The 
upper  plate  was  fastened  to  the  base  of  the  framework  by 

313 


314  CEMENT  AND  CONCRETE 

means  of  two  bolts  which  worked  freely  in  the  lower  plate,  and 
the  latter  was  connected  to  the  weighing  gage  at  the  top  of  the 
framework  by .  two  bolts  which  worked  freely  in  the  upper 
plate.  An  hydraulic  jack  was  placed  under  either  end  of  a 
yoke,  at  the  middle  of  which  was  supported  the  weighing  gage. 
While  the  tensile  and  transverse  tests  are  doubtless  good,  the 
compressive  tests  are  lacking  in  accuracy  because  of  the  crude 
method  of  crushing. 

444.  Table   146  shows   the   comparative   tensile,   transverse 
and  compressive  strengths  of  two  samples  of  cement,  one  of 
Portland  and  one  of  natural,  with  different  proportions  of  sand. 
It  is  seen  that  the  modulus  of  rupture,  or  stress  on  the  extreme 
fiber  in  transverse  tests,  computed  by  the  ordinary  formula,  is 
considerably  greater  than  the  strength  obtained  in  direct  tensile 
tests.     The  ratio  of  the  transverse  to  the  tensile  strength  varies 
from  1.25  to  1.90  for  Portland  and  from  0.95  to  2.19  for  natural. 

4  These  tests  indicate  that  the  ratio  of  the  compressive  strength 
to  the  tensile  strength  diminishes  with  the  addition  of  sand, 
but  the  reverse  has  been  found  to  be  true  in  other  series  of 
tests  where  the  facilities  for  making  compressive  tests  were 
better.  The  result  obtained  here  may  be  attributed  to  the  fact 
that  richer  mixtures  gave  cubes  with  smoother  and  more  regular 
faces,  and  thus  less  subject  to  eccentric  loading.  The  com- 
pressive strength  increases  between  three  months  and  one  year 
much  more  than  the  tensile  and  transverse  strengths.  Tests  on 
ten  brands  of  Portland  and  ten  brands  of  natural  showed  that 
in  general  the  brands  giving  the  highest  strength  in  tension 
gave  also  the  highest  strength  in  transverse  and  compressive 
tests. 

445.  A  few  results  to  show  the  effect  of  consistency  of  the 
mortar  on  the  three  kinds  of  strength  are  given  in  Table  147. 
With  Portland  cement  the  highest  strength  in  transverse  and 
compressive  tests  is  given  by  a  wetter  mortar  than  that  giving 
the  highest  strength  in  tension,  but  with  natural  cement  the 
compressive  strength  is  lowered  more  than  the  tensile  strength 
by  an  excess  of  water.     All  oj  the  specimens  were  one  year 
old  when  broken. 

446.  TRANSVERSE  TESTS  OF  CONCRETE  BARS.  —  The  effect 

on  the  strength  of  concrete  of  variations  in  manipulation  and 
treatment  is  most  satisfactorily  investigated  by  tests  of  large 


MORTAR  AND  CONCRETE 


315 


an 

a 


S 

H 

8  I 

H      tt 

H  S 
H!  a 

n  S 
<3  o 
H  O 

T3 

a 
8 


MEAN  STRENGTH,  POUNDS  PER  SQUARE  INCH,  FOR  VARYING  RICHNESS  OF  MORTARS, 
PARTS  SAND  TO  ONE  OF  CEMENT  BY  WEIGHT. 

T3 
co 

t: 

cS 
OH 
O 

S. 

•    •  o  o             '  t~-  o 

•  S  I-                 _CO  T* 

Trans. 

'  ^  CS                 '  O  -f 
•M  CO                     I-H  7^1 

^ 

.r-  n                .O  CO 

00  O                      -f  -* 

1 

CO 

1 

H 

1 

»c  oo  o  o         •  n  i.o     • 

C:  OO  •*  7-J               ^il- 
«  O  <M  t  -            •  ^  ^      ' 

X 

3 

^r  cT  ^t  oo         .  o  -N     . 

<M  CO  O  iO               I-H  TO 

OD 

1 

'N  t^  00  CS             .  O  1-      . 

1 

00 

1 

O 
H 

& 

I 

4j<      '  CS      '         CO  i-  ^  "N 

I 

t-    '  -ti    '      oo  -N  o  n 

s 

5<    .^h    .     °  ^  co  co 

•d 

1 

£ 

§ 

0 

t 

III!  s  ;i  ; 

i 

H 

o  S  ^  oo      i5     .cb     . 

O   CJ   1-1   »-H            I-H            O 

1 

•ft  o  >-7  oo      o    .00    . 

QC  CO  O'  'N         CS         O 

Neat  Cement. 

g 
O 
O 

CO  t^  I-      •        O  2<  O      • 
c^^^I     .      ^2^     . 

Trans. 

vO  t-  O      *        t—  O  »O 

i-H  CO  "^                   CO  1-  i-H        • 

I-H  -M  CO      '        <N  -*  0      . 

—  —  — 

H 

1IH  :  S^i  : 

£0 

aoy 

ee  es  2  ^      ««  ce  2  ^; 
'O'Cd>>     'd'd  —  >> 

«-»»-  ^g«-, 

•XN3W3Q 

^^^^  ^«^z 

h 

Ed 
ti 

-«"*      o*-co 

o* 

I 

DO 

-d* 


t! 
11 


316 


CEMENT  AND  CONCRETE 


sized  specimens  either  in  compression  or  bending.  In  the  prep- 
aration of  "such  large  specimens  the  conditions  of  actual  con- 
struction may  be  closely  reproduced,  and  the  results,  although 
likely  to  be  quite  irregular,  as  the  strength  of  concrete  in  struc- 
tures is  not  uniform  throughout,  are  nevertheless  very  valu- 
able On  account  of  the  expense  connected  with  such  tests, 
the  number  of  specimens  is  usually  so  limited  that  the  natural 
irregularities  in  strength  mask  the  true  conclusions. 


TABLE   147 

Comparative  Tensile,  Transverse   and    Compressive   Tests, 
of  Varying  Consistency  of  Mortar 


Effect 


TRANSVERSE  AND 

WATER 

MEAN  STRENGTH,  POUNDS  PER 

COMPRESSIVE 

AS  PER 

SQUARE  INCH. 

STRENGTH  AS  PER 

REF. 

CEMENT. 

CENT.  OF 
DRY 

CENT.  OF  TENSILE. 

INGRE- 
DIENTS. 

Tensile. 

Trans. 

Comp. 

Trans. 

Comp. 

1 

P 

9 

516 

837 

1731 

162 

335 

2 

P 

12 

533 

987 

2173 

185 

408 

3 

P 

15 

467 

850 

2498 

180 

533 

4 

P 

18 

461 

966 

2823 

209 

612 

5 

P 

21 

430 

1022 

2487 

239 

578 

6 

N 

12 

272 

447 

2270 

164 

835 

7 

N 

14 

325 

516 

2141 

158 

659 

8 

N 

16 

319 

519 

1481 

163 

464 

9 

N 

20 

304 

509 

1512 

167 

497 

10 

N 

24 

315 

462 

1317 

147 

418 

NOTES:  —Cement,  P  =  Portland,  Brand  R;  N  =  Natural,  Brand  In; 

Sand,  "Point   aux  Pins/'  pass  No.  10  sieve.      Age  of  specimens, 
one  year.     Two  parts  sand  to  one  cement  by  weight. 

In  Tables  148  to  156  are  given  some  of  the  results  obtained 
in  testing  over  two  hundred  concrete  bars  at  St.  Marys  Falls 
Canal.  The  molds  for  making  the  concrete  bars  were  ten 
inches  square  by  four  and  one-half  feet  long  inside.  The  con- 
crete was  rammed  into  the  mold  with  a  light  wooden  rammer. 
The  bars  were,  in  general,  covered  with  moist  earth  soon  after 
completed,  to  await  the  time  of  breaking.  To  break  them  they 
were  supported  on  knife  edges  placed  four  feet  apart,  and  the 
load  was  applied  at  mid-span  through  an  iron  bolt  laid  across 
the  bar.  In  the  earlier  tests  a  direct  load  was  imposed  by  means 
of  a  platform  which  was  gradually  loaded  with  one-man  stone, 
but  in  the  later  tests  the  load  was  applied  by  means  of  hydraulic 


CONCRETE 


317 


jacks,  au  hydraulic  gage  being  used  to  measure  the  force.  In 
many  cases  the  half  bars  were  again  broken  at  a  later  date 
with  a  twenty-inch  span,  as  shown  in  the  tables. 

447.  Variations  in  Richness  of  Mortar.  —  In  Table  148  sev- 
eral concretes  made  with  mortars  having  different  proportions 
of  sand  are  compared,  and  the  results  of  briquet  tests  on  similar 
mortars  are  also  given.  Although  the  briquets  were  not  broken 
at  the  same  age  as  the  bars,  the  tests  on  the  latter  at  the  differ- 
ent ages  show  that  they  were  not  gaining  strength  rapidly, 
and  the  results  may  therefore  be  compared  without  serious 
error. 

TABLE   148 
Transverse    Tests  of  Concrete.      Variations  in  Richness  of  Mortar 


hi 

=  2    3 

MODULUS  OF  RUPTURE. 

No. 
BARS. 

DATE 
MADE. 

CEM- 
ENT. 

*z'z 

!jj*M 

Four  Foot  Sp.'in. 

Twenty  Inch  Span. 

||s 

jipy 

o  cr    « 

No. 
Tests. 

Age. 

Mean. 

No. 

Tests. 

Age. 

Mean. 

Mo.    Da. 

Yr    Mo. 

Yr.  Mo. 

76-77 

11-2 

Port. 

0 

717 

2 

1     7 

503 

4 

2     9 

600 

78-70 

" 

' 

1 

700 

2 

680 

4 

698 

80-81 

u 

« 

2 

505 

2 

538 

4 

677 

82-83 

u 

i 

3 

432 

2 

480 

3 

415 

84-85 

11-3 

« 

4 

335 

2 

370 

4 

385 

86-87 

" 

4 

5 

252 

2 

284 

4 

316 

88-80 

t  ( 

' 

6 

218 

2 

262 

4 

279 

00-01 

11-4 

Nat. 

1 

483 

2 

420 

4 

450 

02-03 

« 

« 

2 

306 

2 

332 

4 

387 

04-0--, 

K 

u 

3 

330 

2 

240 

4 

224 

06-07 

11 

4 

237 

2 

186 

4 

205 

NOTES:  — 

Portland,  Brand  R,  Sample  82  M. 

Natural,  Brand  Gn,  Sample  83  T. 

Sand,  from  *''  Point  aux  Pins"  (river  sand). 

Stone,  Potsdam  sandstone,  retained  on  f  inch  square  mesh,  and  no  pieces 

larger  than  3  inches  in  one  dimension. 
Amount  mortar  used  in  each  case  equal  to  voids  in  stone  measured  loose, 

except  in  case  1-2  natural,  when  mortar  exceeded  voids  by  seven  per 

cent. 
The  fracture  showed  concrete  very  compact  in  nearly  all  cases. 

The  results  obtained  with  natural  cement  show  that  the 
tensile  strength  of  the  mortar  in  pounds  per  square  inch  was 
greater  than  the  modulus  of  rupture  obtained  for  the  concrete. 


318 


CEMENT  AND  CONCRETE 


This  is  also  the  case  with  rich  mortars  of  Portland  cement, 
but  for  Portland  mortars  containing  more  than  three  parts  sand 
to  one  of  cement  the  concrete  gives  the  higher  result.  The 
strength  of  the  concrete  with  one-to-four  mortar  is  fifty-five  per 
cent,  of  the  strength  with  one-to-one  mortar  for  Portland,  and 
forty-five  per  cent,  for  natural.  The  decrease  in  strength  due 
to  larger  proportions  of  sand  in  the  mortar  is  usually  greater 
than  the  decrease  in  cost. 

TABLE    149 
Transverse  Tests  of   Concrete.     Variations  in  Quantity   of  Mortar 


«£« 

«3  H| 

w     w 

MODULUS  OF  RUPTURE. 

No. 
BAR. 

DATE 
MADE. 

SfS  « 

ll«! 

Four  Foot  Span. 

Twenty  Inch  Span. 

H  tfo,  ^ 

<|^ 

jjjj 

No. 
Tests. 

Age. 

Mean. 

No. 
Tests. 

Age. 

Mean. 

Mo.  Da. 

Yr.  Mo. 

42 

7       3 

31 

88 

1 

lyr. 

247 

2 

1    10 

363 

37-40 

7       1 

38 

92 

2 

284 

3 

n 

447 

38-41 

7       1 

47 

104 

2 

« 

350 

4 

n 

596 

39-43 

7    1,3 

60 

112 

2 

" 

346 

4 

t  4 

589 

NOTES:  — 

Cement,  Portland.  Brand  R,  Sample  64  T. 

Sand,  "  Point  aux  Pins,"  three  parts  by  weight  dry  to  one  cement. 
Stone,  Drummond  Island  limestone,  passing  1  inch  slits  and  retained  on 
f  inch  slits. 

448.  Variations  in  Amount  of  Mortar  Used.  —  Bars  37  to 
43,  Table  149,  were  all  made  with  the  same  kind  and  quality 
of  stone  and  the  same  quality  of  mortar,  three  parts  sand  to  one 
cement  by  weight,  but  the  amount  of  mortar  varied;  thus,  in 
bars  41  and  38  sufficient  mortar  was  used   to  fill    the  voids  in 
the  stone,  while  the  bars  above  were  deficient  in  mortar,  and 
those  below  contained  an  excess.     It  is  seen  that  the  highest 
result  is  given  by  the  bars  in  which  the  mortar  was  just  suf- 
ficient to  fill  the  voids  in  the  stone,  though  the  bars  containing 
an  excess  of  mortar  gave  practically  the  same  result,  while  a 
deficiency  of  mortar  resulted  in  decreased  strength. 

449.  Variations  in  the  Amount  of  Sand  for  Fixed  Quantities 
of  Cement  and  Stone.  —  In  Table  150,  bars  68  to  75  were  all 
made  with  the  same  kind  and  quantity  of  cement  and  stone, 
but  the  amount  of  sand,  and  consequently  the  quantity  and 


CONCRETE 


319 


quality  of  the  mortar,  varied.  The  highest  strength  is  given  by 
the  concrete  in  which  the  weight  of  the  sand  was  three  times 
the  weight  of  the  cement;  this  quantity  of  sand  gave  sufficient 
mortar  to  fill  the  voids  in  the  stone.  The  richer  mortars, 
though  stronger,  were  deficient  in  quantity,  while  four  parts 
sand  made  an  oxcess  of  mortar  having  a  lower  strength. 

TABLE  150 

Transverse  Tests  of  Concrete.    Variations  in  Quantity  of  Sand  for 
Fixed  Quantities  of  Cement  and  Stone 


8 

•if. 

^ 

i     a  . 
.2  '«•  9  a 

w  £  w 

MODULUS  OF  RUPTURE. 

pj 

PQ 

& 

0 

P  • 

,-  _ 
<  a 

OQ  W 

U  Eh   O 

-^  <  ft.  K 

-1  W  S  55 

M 
PC 

Four  Foot  Span. 

Twenty  Inch  Span. 

o 

/• 

fc  o 

H  '• 

b***5  g  w 

2;  S^r^ 

H 

w 
a 

K 

0 

0^ 

^ 

|3|§ 

3^ 

'  O  w 

No. 

Tests. 

Age. 

Mean. 

No. 
Tests. 

Age. 

Mean. 

- 

Yr.Mo. 

Yr.Mo. 

74-75 

(').", 

65 

1 

16 

95 

2 

1     8 

299 

4 

2  10 

295 

a 

72-73 

65 

130 

2 

24 

101 

2 

tt    tt 

335 

4 

tt     tt 

303 

6 

70  71 

65 

195 

3 

32 

104 

2 

tt    tt 

324 

4 

tt     tt 

354 

c 

68-69 

65 

260 

4 

42 

110 

2 

«t     tt 

322 

4 

tt     tt 

321 

d 

NOTES:  — 

Cement,  Portland,  Brand  R,  Sample  768. 

Sand,  "  Point  aux  Pins." 

Stone,  Potsdam  sandstone,  screened  with  f  inch  mesh,  and  all  pieces  larger 

than  3  inches  in  one  dimension  rejected. 
Appearance  of  fracture:  a,  very  porous;  6,  many  voids;  c,  some  voids; 

d,  few  voids. 

450.  Consistency   of   Concrete. -- The   bars,   the   results   of 
which  are  given  in  Table  151,  were  made  to  show  the  effect  of 
the  consistency  of  the  concrete  on  the  strength  obtained.     It  is 
seen  that  the  highest  strength  is  given  when  the  consistency 
is  such  that  a  little  moisture  is  shown  when  ramming  is  com- 
pleted; the  decrease  in  strength  from  an  excess  of  water  is  much 
less  than  that  caused  by  a  corresponding  deficiency.     The  re- 
sults of  briquet  tests  on  similar  mortar  are  also  given  in  the 
table,  and  it  appears  that  the  highest  result  is  given  by  the 
mortar  containing  the  least  water,   which  shows  the  familiar 
fact  that  the  mortar  for  concrete  should  be  more  moist  than 
that  which  gives  the  best  results  in  briquet  tests. 

451.  Value  of  Thorough  Mixing.  —  Bars  182  to  189,  Table 
152,  were  made  to  show  the  effect  of  thorough  mixing  of  the 


320 


CEMENT  AND  CONCRETE 


TABLE    151 
Transverse   Tests   of    Concrete.     Variations   in    Consistency 


o  - 

MODULUS  OF  RUPTURE. 

& 

PRO- 

£ 

a  c  • 

k 

o 

CEM- 

PORTIONS. 

Sg  w 

o 
fc 

W 

BAR. 

ENT, 

6 

OH  >^  E^H 

4  Foot  Span, 
13  Months 

20  In.  Span, 
2  Years. 

w 

1 

Kind. 

M 

Z  Pd  pq 

i 

Cem- 

£_, 

Pop 

o 

*3 

ent, 
Lbs. 

Sand, 
Lbs. 

£ 

II" 

No. 
Tests. 

Mean. 

No. 
Tests. 

Mean. 

u 

a 
H 

138-139 

Port. 

120 

237 

0.61 

7.31 

2 

354 

2 

289 

a 

509 

136-137 

120 

237 

0.83 

7.12 

2 

450 

3 

482 

6 

404 

140-141 

120 

237 

1.03 

7.00 

2 

450 

4 

442 

c 

415 

142-143 

120 

240 

1.16 

7.12 

2 

385 

4 

417 

d 

400 

146-147 

Nat. 

115 

230 

0.83 

7.64 

2 

180 

4 

156 

a 

267 

144-145 

115 

230 

1.03 

7.31 

2 

223 

4 

282 

6 

187 

148-149 

115 

230 

1.16 

7.12 

2 

234 

4 

256 

c 

145 

150-151 

115 

230 

1.35 

7.12 

2 

202 

4 

177 

d 

127 

152-153 

115 

230 

1.51 

7.12 

2 

155 

3 

170 

e 

116 

NOTES:  — Portland  cement,  Brand  R,  Sample  M. 

Natural  cement,  Brand  Gn,  Sample  88  T. 

Sand,  "  Point  aux  Pins"  (river  sand). 

Stone,  Potsdam  sandstone,  7  cubic  feet  to  each  batch. 

Results  in  last  column  give  tensile  strength  at  one  year  of  briquets 

made  from  similar  mortar. 
Consistency :  —  a,  very  dry ;  no  moisture  shown  on  ramming. 

6,    slight   moisture   appeared    at    surface    after    continued 
ramming. 

c,  quaked  somewhat. 

d,  quaked  and  water  rose  to  surface  in  ramming, 

e,  too  wet  to  ram. 

TABLE    152 
Transverse  Tests  of  Concrete  Bars.     Value  of  Thorough  Mixing 


MODULUS  OF  RUPTURE. 

No.  BAR. 

MIXING  OF  CONCRETE. 

Four  Foot  Span. 

Twenty  Inch  Span. 

No. 
Tests. 

Age. 

Mean. 

No. 
Tests. 

Age. 

Mean. 

182-186 

Turned  once  and  back 

2 

lyr. 

290 

4 

21^  mo. 

373 

183-187 

"     twice    "        " 

2 

ii. 

294 

4 

u 

353 

184-188 

"  3  times  "        ." 

2 

u 

306 

4 

u 

444 

185-189 

u    4.      tt         u            u 

2 

it 

328 

4 

u 

474 

NOTES:  —Cement,  Portland,  Brand  X,  200  Ibs. 
Sand,  "  Point  aux  Pins,"  600  Ibs. 
Stone,  Potsdam  sandstone,  15  cubic  feet. 


CONCRETE 


321 


concrete.  Comparing  the  concrete  turned  once  or  twice,  and 
back,  with  that  turned  three  or  four  times,  and  back,  it  is  seen 
that  the  mean  strength  of  twelve  tests  with  the  former  is  328 
pounds  per  square  inch,  while  the  mean  strength  of  the  same 
number  of  tests  with  the  more  thoroughly  mixed  concrete  is 
388  pounds  per  square  inch,  an  increase  of  eighteen  per  cent. 

TABLE   153 
Transverse  Tests  of  Concrete.     Variation  in  Size  of  Aggregate 


§ 

STONE. 

s.*  • 

*  X  H 

MODULUS  OF  RUPTURE. 
LBS.  PE»«Sg.  IN. 

No. 
BAU. 

EMENT  SAMI 

AMOUNT  Cr 
icr  STONE  I 
CUBIC  FEE' 

AMOUNT 
RAMMED  Co 
CRETE  MAD 
CUBIC  FEE 

Kind. 

Sizes. 

PER 

CENT. 
VOIDS 

IN" 

COM- 

One Bar,  4 
Ft.  Span, 
Age  1  Yr. 

Half  Bar, 
20  In. 
Span,  Age, 
21  Mo. 

0 

PACT. 

a. 

202 

XRO 

a  * 

V 

45 

3.75 

3  75 

259 

3(57 

199 

t  ; 

a 

J  V,  f  F 

43 

3.75 

3.75 

259 

347 

201 

(4 

a 

M 

44 

3.75 

3.75 

216 

269 

200 

(C 

«} 

\  each, 
Vj  F,  &  M 

}« 

3.75 

3.75 

245 

292 

11)8 

u 

•1 

i  each, 
K,  V,  F,  &  M 

3.75 

3.75 

288 

390 

ire 

XM8 

d 

V 

32 

3.75 

216 

311 

195 

u 

d 

F 

88 

3.75 

3  8fi 

186 

302 

197 

ii 

d 

M 

34 

3.75 

3.75 

131 

208 

194 

" 

'! 

£  each, 
V,  F,  &  M 

j  30 

.  .  . 

.  .  . 

207 

302 

NOTES:  — 

All  mortar,  three  parts  sand  to  one  part  Portland  cement  by  weight. 
Quantity  of  mortar  about  one-third  volume  of  compact  stone. 
Stone:  — a  =  Potsdam  sandstone;  d  =  gravel. 
Size :  —  K  =  T'ff  inch  to  ±  inch. 

V   =   i         "       i     " 

F  =  \        "       1     " 

M  =   1         "      2     " 

452.  Variations  in  Size  of  Stone  and  Volume  of  Voids.  —  The 
bars  given  in  Table  153  were  all  made  with  mortar  composed 
of  three  parts  sand  to  one  of  Portland  cement  by  weight.  The 
stone  for  these  bars  was  sorted  into  different  sizes,  and  these 
were  recombined  in  the  proportions  indicated  in  the  table. 
The  sizes  are  denoted  as  follows:  that  passing  one-half  inch 
mesh  and  retained  on  one-quarter  inch  mesh,  is  called  V;  one- 
half  inch  to  one  inch  is  called  F;  one  inch  to  two  inches,  M; 
two  inches  to  three  inches,  C;  and  coarse  sand,  one-tenth  inch 
to  one-quarter  inch,  is  called  K. 


322  CEMENT  AND  CONCRETE 

The  first  five  bars  were  made  with  broken  sandstone,  and  it 
is  seen  that  the  coarsest  stone,  size  one  inch  to  two  inches, 
gave  the  lowest  result.  The  size  V,  one-quarter  inch  to  one- 
half  inch,  although  containing  no  smaller  percentage  of  voids, 
gave  a  much  higher  strength.  The  highest  result  was  given 
by  the  bar  made  with  a  mixture  of  four  sizes,  the  voids  in  this 
mixture  being  only  thirty-six  per  cent. 

The  bars  containing  gravel  as  aggregate  indicate  that  the 
strength  decreases  as  the  size  of  stone  and  volume  of  voids 
increase,  but  a  mixture  of  three  sizes  gives  nearly  as  good  a 
result  as  the  fine  gravel  alone.  Comparing  the  results  with 
similar  sizes  of  the  two  kinds  of  aggregate,  it  appears  that  the 
broken  sandstone  gives  somewhat  better  results  than  gravel, 
notwithstanding  that  the  proportion  of  voids  in  the  former 
exceeds  that  in  the  latter. 

453.  Sandstone  and  Bowlder  Stone  Compared.  --The  results 
given  in  Table  154  are  from  a  series  of  tests  made  for  the  Mich- 
igan  Lake   Superior   Power   Company   by   Mr.    H.   von   Schon, 
Chief  Engineer,1  and  show  the  strength  of  concretes  made  with 
two   kinds   of   aggregate   available   at   Sault   Ste.    Marie.     Two 
samples  of  Portland  cement,  one  made  from  marl  and  one  from 
limestone,  a   slag   cement,   and   a   natural   cement,  are  used   in 
these  tests. 

The  two  samples  of  Portland  cement  give  nearly  the  same 
result,  the  slag  less  than  half  the  strength,  and  the  natural 
quite  weak.  The  ratio  of  the  strength  obtained  with  crushed 
bowlders  to  that  made  with  sandstone  is  about  1.6  with 
Portland,  and  the  superiority  of  the  former  is  shown  with  all 
cements. 

454.  Various  Kinds  of  Aggregate.  —  Table  155  gives  the  re- 
sults  obtained  at  St.  Marys  Falls  Canal  in  using  various  kinds 
of  stone.     In  bars  25  to  30,  three  kinds  of  stone  are  compared. 
The   superiority  of  the  Kelleys  Island   Limestone  "  shavings " 
from  the  stone  planers  is  evident.     The  shape  of  the  pieces  may 
have  had  a   considerable  influence   on  this   result,   the   planer 
shavings  being  flat,  or  lenticular  in  form.     Bar  34  was  made 
with  a  hard  limestone  from  Drummond  Island,  33  with  gravel, 
and  31  and  32  with  gravel  and  stone  mixed  in  equal  propor- 


Tests  reported  by  H.  von  Schon  in  Trans.  A.  S.  C.  E.,  Vol.  xlii,  p.  135. 


CONCRETE 


323 


TABLE    154 

Transverse  Strength  of  Concrete  with  Crushed  Sandstone  and 

Bowlders 


AGGREGATE. 

MIXTURE  No. 

MODULUS  OF  RUPTURE,  POUNDS  PER  SQUARE  INCH. 

Portland. 
(Marl.) 

Portland. 
(Rock.) 

Slag. 

Natural. 

Sandstone    .     .     . 

u 

U 
U 

1 
2 
3 
4 
5 

328 
283 
220 
178 
106 

312 
205 
178 
173 
186 

122 
161 
118 
74 
131 

43 
34 
40 

'35' 

Mean,  Sandstone    

223 

223 

121 

38 

Bowlder  Stone     . 

1  i             it 

U                            U 
(1                            il 
(4                            U 

1 
2 
3 
4 
5 

407 

377 
332 
327 
333 

397 
395 
374 
351 
325 

145 
167 
176 
146 
123 

36 
67 
55 
52 
60 

Mean,  Bowlder  Stone  .... 

355 

368 

151 

54 

Katio  of  j  Bowlder  Stone  j 

1.59 

1.65 

1.25 

1.42 

Moduli  j      Sandstone      f 

NOTES:  —  Cross  breaking  tests  of  6  in.  by  6  in.  by  24  in.  bars  made  for 
Michigan,  Lake  Superior  Power  Co. 

Materials:  — Cement,  representative  brands  of  each  of  four  classes. 

Sand,  river  sand,  "  Point  aux  Pins,"  mostly  quartz,  96J  Ibs.  per  cubic  foot. 
Voids,  41.7  per   cent.     Fineness,   96  per  cent,   passing    No.   20  sieve, 

39  per  cent,  passing  No.  40  sieve. 
Stone,  Sandstone,  broken  Potsdam  1  to  H  inch  size. 

Bowlder  stone,  broken   gneiss  and  granite   bowlders, 

1  to  l\  inch  size. 

Proportion  in  mortar,  1  part  cement  to  2.4  parts  sand  by  volume. 
Mixing:  — Consistency,  plastic;  cement  and  sand  mixed  dry,  then  wet  and 

mixed;  mortar  added  to  wet  aggregate  and  concrete  mixed  by  hand. 
Storage:  — Bars  stored  in  shed,  protected  from  rain,  fully  exposed  to  air. 

Age  of  specimens  when  broken,  sixty  days. 
Mixture:  —  1.  Mortar  15  per  cent,  in  excess  of  quantity  required  to  fill  voids. 

2.  Mortar  10  per  cent,  in  excess  of  quantity  required  to  fill  voids. 

3.  Mortar  5  per  cent,  in  excess  of  quantity  required  to  fill  voids. 

4.  Mortar  just  sufficient  to  fill  voids  in  stone. 

6.  Mortar  15  per  cent,  in  excess  of  amount  required  to  fill  voids  in 
stone,  but  this  15  per  cent,  excess  made  with  lime  instead  of 
cement. 


324 


CEMENT  AND  CONCRETE 


TABLE  155 
Transverse  Tests  of  Concrete.  Value  of  Different  Kinds  and  Sizes  of  Aggregate 

MODULUS  OF  RUPTURE. 

Twenty  Inch  Span. 

(D 

Aggregate:  —  a  =  Potsdam  sandstone;  size,  f  inch  to  1  inch. 
b  =  Drummond  Island  limestone;  size  f  inch  to  3  inches. 
c  =  Kelleys  Island  limestone;  shavings  from  stone  planers;  size,  £  inch  to  3  inches. 
d  =  Gravel. 
e  —  Broken  brick. 

i*  £o  o  §  cr  o 

CO  CO  ^  ^  CO  CD 

£ 

0 

'2         a  K- 

•  Ss  2  ::;*>> 

::::::&      °?« 

% 

00 

4 

Four  Foot  Span. 

1 

•*O<NTtf«O"*iOfNCsas<NCO 
(MOTfCiOiOaOClCOT-HC'-i 

rH   T-H   <N                    <M   I-H   ,—  1   <M   <M   CO  Tfl 

g 

<3 

£  1- 

1—1                                                         i—  i 
rH 

lj 

PROPORTIONS. 

||£ 
IJ5 

OS                                CD                     O  O 
t--.    -.^^^o^^^oO 

(N                                 CO                     i>-  t~ 

P 

^ 

OS                   T)H                   ^H                           O  O 

i—  1              1-1               i—  i                     <M  (M 

1-S 

IJ 

00 

^  2  -  -  3  2£! 

•aivoaaooy 

'«'« 

?StOO!3hOOfO'ierH|Ci          WO 

i<r«i 

p^HM 

0 

9 
"S 

DO 

-                fe          « 

S  »  2    2    -   GQ2 

0                     «             K 

T3 

3 

•^'  -               -  t3  - 

1  fi  

1 

ir^  OS 

0  0 
>OCDt-OOCiOT^CO(Mr-irYT7 
^(MC^OIiMJOCOCOCOCO^oD 
O  iO 

1—  1    T—  1 

CONCRETE 


325 


tions  The  gravel  and  hard  limestone  gave  about  the  same 
result,  but  it  is  seen  that  the  mixture  gave  a  higher  strength. 
Bars  154  to  159  were  made  to  test  the  value  of  broken  brick  for 
use  in  concrete.  It  is  seen  that  the  strength  obtained  with 
brick  is  considerably  lower  than  that  obtained  with  the  soft 
limestone.  Had  a  poorer  mortar  been  used,  the  brick  would 
doubtless  have  given  a  better  comparative  result,  since  with 
the  one-to-two  mortar,  the  brick  are  not  strong  enough  in  them- 
selves to  utilize  the  full  adhesive  strength  of  the  mortar. 

TABLE    156 

Transverse  Tests  of  Concrete.     Use  of  Screenings  with  Broken 

Stone 


SAND  AND 

STONE. 

STONE 
TO  80  LBS. 

H   . 

tS 

MODULUS  OF  RUPTURE. 

CEMENT. 

J^ 

£ 

No. 

R  4  R 

p 

J2r^ 

FOUR  FOOT 

TWENTY  INCH 

® 

13  AH. 

c? 

*>      ® 

£ 

§ 

"  a* 

a  3 

SPAN. 

SPAN. 

1 

||i 

fj 

4*5 

|| 

^0 

AOE,  11  Mos. 

AGE,  2  YRS. 

S's 

f 

3?  3 

i 

No. 
Tests. 

Mean. 

No. 
Tests. 

Mean. 

114-115 

a 

49 

240 

7.0 

3.43 

3.05 

2 

233 

4 

237 

124-125 

b 

48.4 

243 

7.0 

3.39 

3.05 

2 

196 

4 

210 

112-113 

c 

44 

240 

7.0 

3.08 

2 

194 

3 

236 

1KJ-117 

d 

44 

138 

7.8 

3.43 

2.16 

2 

227 

3 

311 

118-119 

e 

40.5 

243 

7.0 

2.83 

3.10 

2 

201 

4 

219 

120-121 

f 

38.8 

243 

7.0 

2.72 

3.05 

2 

122 

4 

164 

122 

243 

7.0 

3.05 

1 

130 

2 

141 

Screenings  replacing 


NOTES:  — 

Cement:  Natural,  Brand  Gn,  Sample  92  T,  80  Ibs. 
Stone:  —  a  =  Drummond  Island  limestone,  screened. 

6  =  10  parts  screenings  to  100  parts  stone. 

c  =  17  parts  screenings  to  100  parts  stone. 

d  =  17  parts  screenings  to  100  parts  stone. 
equal  amount  sand. 

e  =  50  parts  screenings  to  100  parts  stone. 

/  =  100  parts  screenings  to  100  parts  stone. 

g  =  Screenings  only,  no  broken  stone. 

455.  Use  of  Screenings  with  Broken  Stone.  —  Table  156  gives 
the  results  of  a  number  of  tests  made  to  show  the  effect  of 
mixing  screenings  with  the  broken  stone.  A  smaller  amount 
of  mortar  is  required  to  fill  the  voids  in  a  given  volume  of  stone 
and  screenings  mixed  than  is  required  for  the  same  volume  of 


326  CEMENT  AND  CONCRETE 

stone.  It  is  seen  that,  with  natural  cement,  when  the  same 
volume  of  mortar  is  used  in  the  two  cases,  the  presence  of 
screenings  to  the  amount  of  one-third  of  the  total  aggregate 
does  not  make  a  material  change  in  the  strength  of  the  result- 
ing concrete,  but  when  the  screenings  are  allowed  to  take  the 
place  of  a  part  of  the  sand  in  the  mortar,  as  in  bars  116  and 
117,  a  much  stronger  concrete  results.  Natural  cement  mixed 
with  sand  and  screenings  alone,  bar  122,  does  not  make  a  strong 
concrete,  but  Portland  cement  with  screenings  without  sand 
was  found  to  give  excellent  results. 

456.  Deposition  in  Running  Water.  —  A  few  tests  were  made 
to  show  the  effect  of  depositing  concrete  in  rapidly  running 
water.     The  molds  were  placed  in  the  stream  and  weighted 
down  in  twelve  inches  of  water.     The  concrete  for  two  bars 
was  deposited  as  soon  as  mixed,  that  for  two  other  bars  was 
allowed  to  stand  in  the  air  three  hours  before  deposition,  until 
it  should  have  acquired  an  initial  set,  and  two  bars  were  made 
after  the  mortar  had   been   allowed  to  stand  five  hours  and 
twenty  minutes  before  deposition;  by  this  time  the  mortar  had 
set  quite   hard.      No  attempt  was  made   to  ram  the    concrete, 
which  was  deposited  by  lowering  it  carefully  into  the  water 
with  shovels,  the  molds  being  filled  as  rapidly  as  possible.     A 
very  large  amount  of  the  cement  was  washed  out  by  the  current 
in  all  cases.     After  a  few  months  the  bars  were  removed  from 
the  stream  and  covered  with  earth  as  usual.    The  tests  at  eleven 
months  did  not  appear  to  show  any  advantage  in  allowing  the 
mortar  to  stand  some  time  before  deposition,  but  the  tests  at 
two  years  showed  a  distinct  advantage  in  this  treatment. 

457.  Use  of  Concrete  in  Freezing  Weather.  —  Table  157  gives 
the  results  obtained  with  Portland  cement  concrete  made  in 
the  open  air  during  cold  weather.     The  conditions  as  to  tem- 
peratures and  the  character  of  the  materials  are  fully  given  in 
the  table.     The  experiments  are  too  limited  to  permit  of  draw- 
ing definite  conclusions,  but  the  following  points  are  indicated 
by  the  results  obtained.     The  use  of  warm  water,  100°  to  156° 
Fahr.,  in  freezing  weather  appears  to  give  somewhat  better 
results  than  cold  water.     Salt  should  not  be  used  unless  the 
temperature  is  below  the  freezing  point,  but  in  very  cold  weather 
the  use  of  enough  salt  in  the  water  to  lower  its  freezing  point 
below  the  temperature  of  the  air  seems  to  hasten  the  harden- 


CONCRETE 


327 


TABLE   157 

Transverse  Tests  of  Concrete  Bars.     Use  of  Concrete  in  Low 
Temperatures 


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a,  Concrete  frozen  after  10  to  20  min.;  6,  frozen  in  45  min.;  c,  began  to 
freeze  in  15   min.;  d,  frozen  hard   following  morning  after  mo'ding; 
e,  concrete  still  soft  9  A.M.  morning  after  molding;  /,  bar  defective. 
NOTES: — Cement,  Portland,  Br.  R.    Sand,  "Point   aux   Pins."      Stone, 
Potsdam  sandstone. 


328 


CEMENT  AND  CONCRETE 


ing  as  well  as  to  increase  the  ultimate  strength.     (For  tests  of 
mortars  in  freezing  weather,  see  Art.  50.) 

ART.  58.     RESISTANCE  TO  SHEAR  AND  ABRASION 

458.  Shearing  Strength.  —  The  shearing  strength  of  mortars 
and  concretes  is  of  importance  not  only  because  of  its  intimate 
relation  to  the  compressive  strength,  but  because  of  the  shear- 
ing stresses  to  which  these  materials  are  subjected  in  structures 
reinforced  with  steel.  But  few  tests  of  shearing  strength  have 
been  made,  however,  partly  because  of  the  lack  of  appreciation 
of  their  value,  and  partly  because  it  is  difficult  to  subject  a 
specimen  to  a  purely  shearing  stress.  It  is  frequently  stated 
that  the  shearing  strength  is  somewhat  in  excess  of  the  tensile 
strength,  perhaps  as  much  as  twenty  per  cent. 

Table  158  gives  the  results  of  a  series  of  tests  made  by  Prof. 
Bauschinger  in  1878.1  The  values  in  shear  are  very  closely 
twenty  per  cent,  in  excess  of  the  tensile  strengths  of  similar 
mortars  tested  at  the  same  time. 

TABLE    158 

Shearing   Strength   of   Portland   Cement   Mortar   Cubes   Hardened 

in  Air 


SHEARING  STRENGTH,  POUNDS  PER 

KZ    . 

SQUARE  INCH. 

TENSILE 

CEMENT. 

gg§ 

Age  of  Mortar. 

OP  SIMILAR 
MORTARS 

s§£ 

AT  EIGHT 

WEEKS. 

|DQ 

1  week. 

2  weeks. 

4  weeks. 

8  weeks. 

Quick    setting    Port-  ( 

None 

225 

270 

257 

259 

210 

land,  mean  results  < 

3 

108 

128 

154 

196 

169 

of  four  brands.         ( 

5 

67 

94 

112 

168 

139 

Slow  setting  Portland,  ( 

None 

301 

323 

341 

377 

256 

mean  results  of  four  ) 

3 

124 

164 

199 

237 

181 

brands.                       ( 

5 

78 

122 

138 

199 

169 

NOTE: — Cement,  each  result  mean  of  four  brands.     Sand,  medium  grain, 

clean.     Mortars  hardened  in  dry  air. 
Tests  by  Professor  Bauschinger,  1878. 

459.  A  distinction  should  be  drawn  between  the  resistance 
offered  by  a  thin  mortar  bed  to  the  sliding  of  one  stone  or  brick 
on  another  and  to  shear  of  the  mortar  itself.  The  former  re- 


Quoted  by  Mr.  Emil  Knichling  in  a  Report  on  Cement  Mortars. 


SHEAR  AND  ABRASION  329 

sistance  involves  the  adhesion  of  the  mortar  to  the  surface  of 
the  brick  or  stone,  and  the  values  for  this  resistance  are  usually 
much  less  than  the  shearing  strength,  and  not  greatly  in  excess 
of  the  adhesive  strength.  The  one  is  of  importance  in  the  de- 
termination of  the  stability  of  masonry  dams,  retaining  walls, 
etc.,  but  the  latter  is  the  resistance  in  question  in  the  design 
of  monolithic  concrete  structures. 

460.  Resistance    to    Abrasion.  —  The    resistance    of    cement 
mortar  to  abrasion  depends  on  the  quality  of  the  sand  as  well 
as  the  cement.     The  abraiding  surface  wears  away  the  cement 
or  pulls  the  particles  of  sand  out  of  their  beds  in  the  cement 
matrix.     If  the  adhesion  to  the  sand  grains  is  strong,  the  sand 
particles  receive  the  wear  and  withstand  it  until  nearly  worn 
away.     With  hard  sand  particles,  therefore,  the  resistance  to 
abrasion  should  increase  as  the  proportion  of  sand  increases, 
until  the  volume  of  the  cement  matrix  becomes  relatively  too 
small  to  thoroughly  bind  the  sand  grains  together.    This  limit  is 
reached,  however,  when  the  mortar  contains  not  more  than  two 
parts  sand.     With  soft  sand  grains,  the  neat  cement  will  usually 
give  the  highest  resistance  to  abrasion,  at  least  in  the  case  of 
Portland.     It  has  been  found  that  specimens  hardened  in  the  air 
are  brittle  and  wear  more  rapidly  than  those  hardened  in  water. 

461.  Table   159  gives  the  results    of  several  tests  made  to 
determine  the  relative  wearing  qualities  of  different  mortars  for 
such  uses  as  sidewalk  construction.     The  specimens  were  two- 
inch  cubes,  hardened  in  water  and  dried  for  a  few  hours  just 
before  grinding.     An  emery  plate,  set  horizontally,   was  used 
in  most  of  the  tests.     The  results  in  any  given  line  of  the  table 
are  comparable,  but,  owing  to  changes  in  the  grinding  plate 
and  in  the  methods  used,  the  results  in  different  lines  are  not 
all  intercomparable.     It  is  seen  that  when  soft  sand  is  used, 
such  as  limestone  screenings,  the  greatest  resistance  to  abrasion 
is  offered  by  the  neat  cement  mortar,  and  the  resistance  de- 
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hard  sand,  such  as  the  siliceous  river  sand,   from   Point  aux 
Pins  ("P.P."  in  the  table)  is  employed,  the  greatest  resistance 
is  offered  by  mortars  containing  about  equal  parts  of  sand  and 
cement.     A  comparison  of  lines  5  and   10  indicates  that  rich 
natural  cement  mortars  lose  about  twice  as  much  as  similar 
mortars  of  Portland,   but  natural  cement  mortars   containing 


330 


CEMENT  AND  CONCRETE 


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EXPANSION  AND  CONTRACTION 


331 


more  than  two  parts  by  weight  of  sand  do  not  give  relatively 
as  good  results. 

ART.  59.     THE  EXPANSION  AND  CONTRACTION  OF  CEMENT  MOR- 
TAR, AND  THE  RESISTANCE  OF  CONCRETE  TO  FIRE 

462.  Change  in  Volume  during  Setting.  —  Cement  mixtures 
shrink  somewhat  when  hardened  in  air,  while  specimens  stored 
in  water  expand  a  trifle  during  hardening.  Although  several 
experiments  have  been  made  on  this  subject  the  specimens  used 
have  been  so  small  that  the  results  obtained  by  various  author- 
ities do  not  agree,  and  the  effect  of  variations  in  the  character  of 
the  mixtures  has  not  been  thoroughly  investigated.  The  impor- 
tance of  the  question  is  found  in  the  necessity  of  providing  ex- 
pansion joints  in  long  walls  or  sheets,  and  in  the  effect  of  such 
changes  in  volume  in  producing  initial  stresses  in  concrete  or 
steel  where  these  materials  are  used  in  combination. 

Certain  general  conclusions  are  well  established  and  may  be 
stated  as  follows:  1st.  The  shrinkage  of  mortar  and  concrete 
hardening  in  air  is  considerably  greater  than  the  expansion  of 
similar  specimens  hardening  in  water;  2d.  The  amount  of 
change  in  volume  increases  with  the  proportion  of  cement  used 
in  the  mixture;  3d.  The  change  in  volume  is  continuous  up  to 
one  year,  but  about  one  half  of  the  change  occurs  in  the  first 
week,  and  it  is  very  slow  after  3  to  6  months. 

The  following  values  of  the  change  in  linear  dimensions  are 
derived  from  the  results  of  several  experimenters,  and  show  in  a 
general  way  what  changes  are  to  be  expected  at  the  end  of  three 
months.1  Variations  in  the  character  of  the  cement  and  the 
consistency  of  the  mortar  will  affect  the  result. 


COMPOSITION:  PARTS  SAND 
TO  ONE  PORTLAND 
CEMENT. 

SHRINKAGE  OF  MORTARS 
HARDENED  IN  AIR. 

EXPANSION  OF  MORTARS 
HARDENED  IN  WATER. 

CHANGE  IN  LINEAR  DIMENSIONS,  ONE  UNIT  IN 

Neat  cement    .... 
One  part  sand  .... 
Three  parts  sand  .     .     . 

300  to    800 
600  to  1200 
700  to  1200 

500  to  2000 
1200  to  3000 
3000  to  5000 

1  For  more  detailed  results  the  reader  is  referred  to  the  following  authori- 
ties:—Dr.  Tomei,  Trans.  A.  S.  C.  E.,  Vol.  xxx,  p.  16.  Mr.  John  Grant, 
Proc.  Inst.  C.  E.,  Vol.  Ixii,  p.  108.  Prof.  Bauschinger,  Trans.  A.  S.  C.  E. 
Vol.  xv,  p.  722. 


332  CEMENT  AND  CONCRETE 

463.  The  Coefficient  of  Expansion  of  Cement  and  Concrete.  — 

Concerning  the  coefficient  of  expansion  of  cement  mortars  of 
various  compositions,  we  know  but  little.  The  result  obtained 
by  M.  Bonniceau,  giving  the  coefficient  of  neat  Portland  cement 
as  about  .000006  per  degree  Fahr.,  is  frequently  quoted.  This 
is  very  nearly  the  value  for  iron  and  steel,  and  has  formed  a  the- 
oretical basis  for  combining  these  materials.  In  the  case  of 
cement  mortars  and  concretes,  however,  it  is  highly  probable 
that  the  coefficient  follows  quite  closely  the  behavior  of  the  sand 
and  stone  used  in  the  mixture,  and  is  much  less  dependent  upon 
the  coefficient  of  the  cement.  This  was  indicated  by  the  results 
of  M.  Bonniceau  who  obtained  a  value  of  about  .000008  for  con- 
crete. 

464.  A  number  of   experiments  to  determine  the  coefficient 
of  expansion  of  cement  concretes  were  carried  out  under  the 
direction  of  Prof.  Wm.  D.  Pence  by  students  of  Purdue  Uni- 
versity.1    As  a  mean  of  seven  tests  with  one-two-four  concrete 
of   Bedford   oolitic   and    Kankakee   limestones    combined   with 
Portland  cements  of  two  well-known  brands,  the  mean  result 
for  the  coefficient  was  .0000055,  the  lowest  result  being  .0000052, 
and  the  highest  result  .0000057.     The  coefficient  of  a  bar  cut 
from  the  Kankakee  limestone  was  .0000056,  the  same  result  as 
obtained  from  the  mean  of  three  tests  of  concrete  containing 
broken  stone  of  this  variety. 

The  average  result  of  four  tests  of  gravel  concrete  composed 
of  one  part  Portland  cement,  two  parts  sand  and  four  parts 
screened  gravel,  or  one  part  Portland  cement  to  five  parts  un- 
screened gravel,  gave  .0000054  as  the  coefficient  of  expansion. 

These  values  differ  from  the  coefficient  of  steel  enough  to 
indicate  that  in  positions  where  the  range  in  temperature  is 
great,  the  resulting  stresses  in  the  concrete  and  steel  may  be 
considerable,  and  worthy  of  attention. 

465.  THE  FIRE-RESISTING  QUALITIES  OF  CONCRETE.  —  The 

value  of  concrete  as  a  material  to  be  used  in  the  construc- 
tion of  the  walls  and  floors  of  buildings,  is  largely  dependent 
on  its  fire-resisting  qualities.  That  its  use  for  such  purposes 
is  rapidly  extending,  is  some  evidence  that  these  qualities  are 


1  Paper  read  before  the  Western  Society  of  Engineers,  Engineering  News, 
Nov.  21,  1901. 


REMHTANCE   TO  FIRE  333 

as  satisfactory  as  in  other  classes  of  materials  devoted  to  the 
same  use. 

Under  favorable  circumstances,  a  fire  in  a  building  filled  with 
combustible  materials  may  reach  a  temperature  of  2,000°  to 
2,300°  Fahr.  If  a  small  specimen  of  cement  mortar  or  concrete 
is  subjected  to  a  temperature  approaching  this  intensity,  the 
cement  loses  its  water  of  crystallization  and  becomes  friable. 
If  cooled  suddenly  in  water,  the  specimen  cracks  and  disinte- 
grates. If  cooled  gradually,  the  outer  edge  of  the  specimen 
crumbles  away.  From  such  tests  on  small  specimens  some  very 
erroneous  conclusions  have  been  drawn  as  to  the  value  of  con- 
crete as  a  fire-resisting  material.  Such  conclusions  have  done 
much  to  prejudice  the  public  mind  against  concrete,  and  to  re- 
tard its  introduction  in  buildings  designed  to  be  fireproof. 

466.  Conductivity.  —  The  great  value  of  concrete  as  a  fire 
resistant  is  due  to  its  low  conductivity  of  heat,  and  while  the 
surface  of  a  mass  of  concrete  exposed  to  an  intense  flame  for 
some  time  is  ruined,  and  may  be  flaked  off  by  the  application 
of  a  strong  stream  of  water  from  a  fire  hose,  the  depth  to  which 
the  heat  penetrates  is  very  limited.  Steel  is  said  to  lose  ten 
per  cent,  of  its  strength  at  about  600°  Fahr.  and  fifty  per  cent, 
at  about  750°  Fahr.  The  importance  of  protecting  the  steel 
framework  of  a  building,  not  only  from  warping  and  complete 
destruction  due  to  flames,  but  from  loss  of  strength  from  over- 
heating, is  therefore  evident. 

Among  engineers  and  architects  it  is  recognized  that  the 
term  " fireproof  construction"  is  only  relative,  although  the 
lay  mind  is  apt  to  give  a  definite  and  literal  meaning  to  the 
term.  It  is  well  known  that  fireproofing  tile,  whether  hard  or 
porous,  will  fall  to  pieces  if  subjected  to  a  temperature  above 
that  employed  in  its  manufacture.  The  practical  question  then 
is,  what  type  of  construction  will  withstand  long  continued 
intense  flame,  and  subsequent  quenching  with  water,  with  the 
least  injury  to  the  strength  of  the  structure.  The  results  of 
fire  tests  that  have  been  conducted  in  several  places,  and  no- 
tably those  made  by  the  Department  of  Buildings  of  New  York 
City,  have  shown  that  floor  arches  properly  constructed  of 
concrete-steel  are  equal  to  any  style  of  floor  with  which  they 
come  in  competition. 

The  low   conductivity  of    concrete  is  shown    by  the  fact, 


334  CEMENT  AND  CONCRETE 

stated  by  Mr.  Howard  Constable  in  connection  with  the  dis- 
cussion of  fire  tests  of  concrete  floor  arches,1  "  that  in  some 
thirty-five  cases  where  the  temperature  ranged  from  1,500  to 
2,400  degrees,  the  time  of  exposure  being  from  one  to  six  hours, 
the  temperature  of  the  upper  flanges  of  six-inch  to  ten-inch 
beams  might  be  approximately  place~d  at  not  much  above  200 
degrees."  He  also  says  "in  one  case,  where  the  beam  was  pro- 
tected by  three  inches  of  concrete,  the  fire  was  maintained  for 
five  hours,  and  the  temperature  went  as  high  as  2,300  degrees, 
and  there  was  no  practical  or  permanent  set  produced  in  the 
beams." 

467.  Behavior   in  Conflagrations.  —  As  to   the  behavior  of 
concrete-steel  arches  in  an  actual  fire,  a  board  of  experts  was 
appointed  by  the  insurance  companies  to  investigate  the  causes 
and  extent  of  damage  to  the  fireproof  buildings  in  the  Pitts- 
burg,   Pa.,   fire  of  May  3,    1897.     This  board  stated  in  their 
report  that  they  believed  that  in  important  structures  of  this 
class  "the  fireproofing  should  be  in  itself  strong  and  able  to 
resist  severe  shocks,  and  should  if  possible,  be  able  to  prevent 
the  expansion  of  the  steel  work  ";  and  continued,  "There  seems 
to  be  but  one  material  that  is  now  known  that  could  be  utilized 
to   accomplish  these   results,   and   that  is   first-class   concrete. 
The  fire-resisting  qualities  of  properly  made  concrete  have  been 
amply  proven  to  be  equal,  if  not  better    than  fire  clay  tile,  as 
shown  by  the  tests  carried  on  by  the  Building  Department  of 
the  City  of  New  York." 

468.  In  a  report  on   the    Baltimore    fire,  Captain    Sewall,2 
Corps  of  Engineers,  U.  S.  A.,  says  concrete  "undergoes  more  or 
less  molecular  change  in  fire;  subject  to  some  spalling.     Molecu- 
lar  change   very  slow.     Calcined   material   does   not   spall   off 
badly,   except  at  exposed  square   corners.     Efficiency  on  the 
whole  is  high.     Preferable  to  commercial  hollow  tiles  for  both 
floor  arches  or  slabs  and  column  and  girder  coverings.     In  form 
of  reinforced  concrete  columns,  beams,  girders  and  floor  slabs, 
at  least  as  desirable  as  steel  work  protected  with  the  best  com- 
mercial  hollow   tiles.     Stone   concrete   spalls   worse   than   any 


1  Trans.  A.  S.  C.  E.,  Vol.  xxxix,  p.  149. 

2  Report  to  the  Chief  of  Engineers,   U.  S.  A.,  by  Capt.  John  Stephen 
Sewail,  Corps  of  Engineers,     Published  in  Engineering  News,  March  24, 1904. 


RESISTANCE   TO  FIRE  335 

other  kind,  because  the  pieces  of  stone  contain  air  and  moisture 
cavities,  and  the  contents  of  these  rupture  the  stone  when 
hot.  Gravel  is  stone  that  has  had  most  of  these  cavities  elimi- 
nated by  splitting  through  them,  during  long  ages  of  exposure 
to  the  weather.  It  is  therefore  better  for  fire-resisting  concrete 
than  stone.  Broken  bricks,  broken  slag,  ashes  and  clinker  all 
make  good  fire-resisting  concrete.  Cinders  containing  much 
partly  burned  coal  are  unsafe,  because  these  particles  actually 
burn  out  and  weaken  the  concrete.  Locomotive  cinders  kill 
the  cement,  besides  being  combustible.  On  the  whole,  cinder 
concrete  is  safe  only  when  subjected  to  the  most  rigid  and 
intelligent  supervision;  when  made  properly,  of  proper  ma- 
terials, however,  it  is  doubtful  whether  even  brickwork  is  much 
superior  to  it  in  fire-resisting  qualities,  and  nothing  is  superior 
to  it  in  lightness,  other  things  being  equal." 

469.  Aggregate  for  Fireproof   Work.  —  Since  air  is  a  poor 
conductor  of  heat,  the  more  porous  concretes  are  the  better 
protectors  against  fire.     On  this  account,  as  well  as  because  of 
its  lightness,  cinder  concrete  is  preferred  for  fireproofing.     Care 
should  be  taken  that  cinders  to  be  used  in  fireproofing  concrete 
do  not  contain  any  appreciable  amount  of  unburned  coal;  in 
concrete  to  be  used  next  to  steel  members  the  cinders  should 
also  be  practically  free  from  iron  rust.     (See  §473.) 

The  strength  of  cinder  concrete  is  much  inferior  to  that 
made  with  the  ordinary  aggregates,  and  there  should  be  no 
difficulty  in  making  a  porous  concrete  with  the  latter.  In  fact, 
in  many  other  classes  of  construction  it  has  been  seen  that 
great  precautions  must  be  taken  to  avoid  porosity.  By  the 
use  of  insufficient  mortar  to  fill  the  voids  in  the  stone,  voids 
may  be  left  in  the  concrete,  though  a't  the  expense  of  dimin- 
ishing somewhat  the  strength  of  the  mixture.  In  adopting  such 
an  expedient  one  should  not  lose  sight  of  the  fact  that  in  order 
to  preserve  the  imbedded  steel  from  corrosion,  it  must  be  fully 
covered  with  the  mortar. 

470.  Broken  bricks  are  excellent  for  fireproofing  concrete. 
The  bricks  themselves  are  fire  resistant,  porous  and  light,  while 
the  adhesion  of  cement  mortar  to  bricks  is  so  great  that  unless 
a  very  weak  mortar  is  used,  the  strength  of  the  concrete  is 
limited  only  by  the  strength  of  the  brick  employed. 

Sandstones,   especially   those   with .  siliceous  cementing  ma- 


336  CEMENT  AND  CONCRETE 

terial,  are  also  well  adapted  for  this  purpose.  Limestone,  on 
account  of  the  low  temperature  at  which  it  is  broken  up,  is 
not  good,  though  as  to  just  how  far  a  limestone  concrete  would 
be  disintegrated  by  the  heat  of  an  ordinary  building  fire  has 
not,  so  far  as  the  author  knows,  been  fully  investigated.  It  is 
known,  however,  that  limestone  masonry  is  calcined  to  a  cer- 
tain depth  in  a  conflagration. 

Granite  in  large  pieces  is  cracked  by  only  a  moderate  degree 
of  heat,  and  spalls  badly.  Just  how  much  danger  there  might 
be  of  a  similar  action  in  concrete  aggregates  of  this  material  is 
not  known,  nor  whether  small  pebbles  or  fine  gravel  would 
have  this  property  in  the  same  degree,  though  it  is  believed 
they  would  not,  and  this  view  has  been  confirmed  by  observa- 
tions of  the  Baltimore  ruins. 

Before  adopting  a  given  aggregate  for  fireproof  work,  one 
should  satisfy  himself  by  actual  test  as  to  the  suitability  of  the 
materials  available,  but  such  tests  should  be  conducted  upon 
concretes  containing  the  proposed  aggregates,  rather  than  upon 
fragments  of  the  materials  not  incorporated  with  mortar. 

ART.  60.   THE  PRESERVATION  OF  IRON  AND  STEEL  BY  MORTAR 

AND  CONCRETE 

471.  The  rusting  of   steel  members  in  modern  buildings  and 
other  engineering  structures  is  one  of  the  most  serious  menaces 
to  their  permanence.      The  introduction  of   concrete-steel  con- 
struction has   given  rise  to   some   discussion,  especially  among 
those    unfamiliar  with  the   properties    of   concrete,   as    to    the 
effect  of  the   concrete  upon  the  steel. 

472.  Action  of  Corrosion.  —  The  rusting  of  iron  takes  place 
only  in  the  presence  of  moisture,  air  and  carbon  dioxide.     In 
perfectly  dry  air,  or  in  perfectly  pure  water,  iron  does  not  rust. 
Under   the   proper   conditions,    however,    the   iron,    water   and 
carbonic  acid  combine  to  form  ferrous  carbonate,  which  at  once 
combines  with  oxygen  from  the  air  to  form  ferric  oxide,  the 
carbonic  acid  being  liberated  to  act  on  a  fresh  portion  of  the 
metal.     It  is  seen  that  only  a  very  small  amount  of  the  carbon 
dioxide  is  necessary.     If,  however,  the  carbon  dioxide  or  other 
acid  filling  the  same  role,  is  neutralized  by  the  presence  of  an 
alkaline  substance,  the  foregoing  reactions  cannot  take  place. 
As  cement  is  strongly  alkaline,  it  thus  furnishes  an  almost  per- 
fect protection  against  rusting. 


t 
EFFECT  ON  CORROSION  OF  METAL  337 

473.  Tests  of  Effect  of   Concrete  on  Corrosion  of  Metal.  - 

To  determine  the  cause  of  occasional  rusting  of  steel  surrounded 
by  cinder  concrete,  and  consequently  the  proper  methods  of 
applying  cement  mortar  or  concrete  to  steel,  Prof.  Chas.  L. 
Norton,  engineer  in  charge  of  the  Insurance  Engineering  Ex- 
periment Station  at  Boston,  made  tests  on  several  hundred  bri- 
quets in  which  steel  was  imbedded  in  mortars  and  concretes 
of  various  compositions.1  The  briquets  were  subjected  to  air, 
steam  and  carbon  dioxide,  others  to  air  and  steam,  to  air  and 
carbon  dioxide  and  to  the  ordinarily  dry  air  of  a  room.  At  the 
end  of  three  weeks  it  was  found  that  neat  Portland  cement  had 
furnished  a  perfect  protection  in  all  cases.  The  corrosion  of 
the  steel  in  other  specimens  was  always  at  a  point  where  a  void 
existed  in  the  concrete,  or  where  a  badly  rusted  cinder  had  lain. 
In  every  case  where  the  concrete  or  mortar  had  been  mixed  wet, 
and  the  surface  of  the  steel  had  been  thus  coated  with  a  thin 
layer  of  grout,  no  rust  spots  occurred. 

In  the  first  tests  made  by  Professor  Norton  the  specimens 
were  thoroughly  cleaned  before  being  imbedded  in  the  concrete, 
but  later  tests  indicated  that  in  specimens  that  had  begun  to 
corrode  before  treatment,  the  rusting  was  arrested  by  the  coat- 
ing of  cement  mortar  or  concrete.  After  from  one  to  three 
months  in  tanks  holding  steam  and  carbon  dioxide,  specimens 
which  had'  been  in  all  stages  of  corrosion  before  being  im- 
bedded in  the  concrete  had  not  suffered  any  sensible  change 
in  weight  or  size  except  when  the  concrete  had  been  poorly 
applied. 

474.  The  results  of  these  experiments  showed  that  the  steel 
need  not  necessarily  be  freed  from  rust  before  being  imbedded 
in  the  concrete;  that  the  concrete  to  be  applied  next  the  steel 
should  be  mixed  wet,  or  that  the  steel  should  be  first  coated 
with  grout  by  dipping  or  brushing;  and  it  appeared  that  the  rust- 
ing sometimes  found  in  cinder  concrete  is  due  to  the  rust  in  the 
cinders  rather  than  to  the  sulphur,  and  that  if  proper  precau- 
tions are  taken,  cinder  concrete  is  nearly  as  effective  as  stone 
concrete  in  preventing  corrosion.     Prof.  Norton  says,  "In  the 
matter  of  paints  for  steel  there  is  a  wide  difference  of  opinion. 
I   cannot  believe   that  any  of    the    paints    of    which  I  have 


Report  III  of  Insurance  Engineering  Exp.  Station,  Boston,  Mass. 


338  CEMENT  AND  CONCRETE 

any   knowledge    can    compare   with  a  wash  or  painting   with 
cement.'' 

475.  Sulphur  in  Cinders.  —  The  conclusions  drawn  by  Booth, 
Garrett  and  Blair  from  a  series  of  tests  made  for  the  Roebling 
Construction  Co.,  were  that  cinders  from  anthracite  pea  coal 
contained  about  two-tenths  per  cent,   of    sulphur  which  they 
considered   sufficient   to   cause    corrosion  of   unprotected    iron- 
work, more  or  less  rapidly,  depending  on  the  presence  or  absence 
of  moisture;  but  they  further  concluded  that  a  "full"  concrete 
(one  in  which  the  voids  in  the  cinders  were  entirely  filled  by 
mortar  of  cement  and  sand)  would  fully  protect  the  steel. 

In  a  paper  read  before  the  Associated  Expanded  Metal  Com- 
panies, Prof.  S.  B.  Newberry  has  this  to  say  concerning  cinder 
concrete:  1  "The  fear  has  sometimes  been  expressed  that  cinder 
concrete  would  prove  injurious  to  iron,  on  account  of  the  sulphur 
contained  in  the  cinders.  The  amount  of  this  sulphur  is,  how- 
ever, extremely  small.  Not  finding  any  definite  figures  on  this 
point,  I  determined  the  sulphur  contained  in  an  average  sample 
of  cinders  from  Pittsburg  coal.  The  coal  in  its  raw  state  con- 
tains rather  a  high  percentage  of  sulphur,  about  fifteen  per 
cent.  The  cinders  proved  to  contain  only  0.6  per  cent,  sulphur. 
This  amount  is  quite  insignificant,  and  even  if  all  oxidized  to 
sulphuric  acid,  it  would  at  once  be  taken  up  and  neutralized 
in  concrete  by  the  cement  present,  and  could  by  no  possibility 
attack  the  iron." 

476.  Precautions.  —  While  so  far  as  the  corrosion  of   steel 
is  concerned,  the  above  experiments  by  Prof.  Norton  show  that 
the  rusting  is  corrected  by  the  concrete,  yet  it  is  quite  possible 
that  the  adhesion  of  cement  to  steel  may  be  impaired  by  a  coating 
of  rust.     The  cleaning  of  the  steel  may  be  accomplished  by 
first  brushing  with  wire  brushes  to  remove  all  scales,  followed 
by  treatment  with  hot  dilute  sulphuric  acid,  and  finally  apply- 
ing an  alkaline  wash  such  as  hot  milk  of  lime  to  neutralize  all 
traces  of  the  acid.     Oxalic  acid  may  be  used  in  place  of  the 
sulphuric,  and  the  application  of  the  milk  of  lime  dispensed  with, 
since  the  acid  oxidizes.     The  crystals  of  oxalic  acid  as  purchased 
commercially  should  be  mixed  with  about  seven  parts  hot  water 
and  the  solution  applied  with  a  brush  or  sponge.     When  the 


Engineering  News,  Apr.  24,  1902. 


f 

PRESERVATION  OF  STEEL  339 

adhesion  of  the  mortar  or  concrete  to  the  steel  is  of  any  impor- 
tance, as  it  is  in  all  concrete-steel  construction  where  the  stresses 
are  divided  between  the  steel  and  concrete,  any  of  the  ordinary 
oil  paints  will  not  only  be  quite  unnecessary,  but  may  be  a  very 
serious  detriment  to  the  construction. 

The  experiments  quoted  indicate  the  importance  of  having 
the  steel  covered  with  an  unbroken  coating  of  cement  or  cement 
mortar.  To  insure  this  the  steel  must  either  be  coated  with  a 
layer,  preferably  of  neat  Portland,  by  dipping  or  brushing,  or 
the  mortar  placed  next  the  steel  must  be  wet  enough  to  insure 
intimate  contact  throughout.  It  may  be  added  also,  that  the 
addition  of  a  small  amount  of  thoroughly  slaked  lime  to  Port- 
land cement  mortar  or  concrete  will  not  only  render  the  mate- 
rial more  alkaline,  but  will  make  the  mortar  more  plastic,  and 
thus  insure  a  better  coating  of  the  steel.  Such  small  additions 
have  no  deleterious  effect  on  the  mortar. 

477.  Practical  instances  of  the  preservation  of  iron  by  con- 
crete are  not  wanting.  The  writer  has  stored  in  water,  briquets 
with  small  iron  plates  imbedded  in  Portland  cement  mortar, 
and  at  the  end  of  six  months  the  plates  were  found  moist,  but 
entirely  free  from  corrosion  except  where  they  projected  beyond 
the  mortar.  A  concrete-steel  water  main  built  on  the  Monier 
system  at  Grenoble,  France,  was  taken  out  and  examined  after 
fifteen  years  service  in  damp  ground.  The  metal  imbedded  in 
the  mortar  showed  no  signs  of  corrosion,  and  the  mortar  could 
only  be  detached  from  it  by  hammering. 

Mr.  W.  G.  Triest *  relates  that  in  breaking  up  cast-iron,  con- 
crete-filled pillars,  a  wrench  was  found  that  had  been  buried 
in  the  concrete  for  twenty-two  years.  The  wrench  had  main- 
tained its  metallic  surface  in  the  concrete,  while  a  part  of  it  that 
had  been  imbedded  in  coal  ashes  had  corroded  badly. 

Similar  instances  showing  the  action  of  concrete  on  steel 
and  iron  might  be  multiplied,  but  it  is  sufficient  to  state  that 
the  preservation  of  iron  or  steel  properly  imbedded  in  Port- 
land cement  mortar  or  concrete  is  now  seldom  questioned,  and 
the  use  of  cement  paint,  in* place  of  the  ordinary  oil  paints, 
as  a  steel  preservative,  has  been  adopted  in  many  places. 


1  Trans.  A.  S.  C.  E.,  April,  1894. 


340  CEMENT  AND  CONCRETE 

ART.     61.     POROSITY     AND     PERMEABILITY;     EFFLORESCENCE; 
POINTING;  USE  u;  SEA  WATER 

478.  The  porosity  and  permeability  of  mortars  have    been 
thoroughly  investigated   by  M.  Paul   Alexandre,  who  has  pub- 
lished his  results  in  "  Recherches  Experimentales  Sur  Les  Mortiers 
Hydr antiques"  l     The  results  and    conclusion  in  the  following 
notes   on   the   subject   are  largely  a  resume  of    the  systematic 
investigation  made  by  M.  Alexandre. 

The  two  qualities,  porosity  and  permeability,  should  not  be 
confused,  nor  should  it  be  thought  that  a  porous  mortar  is 
always  very  permeable,  or  that  a  permeable  mortar  must  of 
necessity  be  very  porous.  Porosity  is  measured  by  the  amount 
of  water  which  will  be  absorbed  by  a  specimen  after  drying, 
while  permeability  is  measured  by  the  amount  of  water  which 
will  pass  through  a  specimen  in  a  given  time  under  certain  de- 
fined conditions  of  thickness,  water  pressure  and  area  of  face. 

479.  Porosity.  —  The  porosity  of   mortars  is  due  to,  and  in 
fact  is  measured  by,  the  volume  of  the  voids  contained.     These 
voids  may  be  divided  into  three  classes,  according  to  the  causes 
to  which    they  may  be  attributed,   as   follows:   1st,  apparent 
voids,  due   to  the   mortar  not   being   properly   compacted;   2d, 
latent  voids   due  to  the  imprisonment  of  air  in  the  mortar  when 
made;  and  3d,  voids  resulting  from  the  evaporation,  during  har- 
dening, of  a  portion  of  the  water  used  in  gaging. 

480.  Apparent  voids  may  occur  as  the  result  of  using  insuf- 
ficient cement  to  fill  the  voids  in  the  sand,  or,  in  the  case  of 
concretes,  insufficient  mortar  to  fill  the  voids  in  the  aggregate. 
They  may  also  be  due  to  improper  manipulation  as  to  tamping, 
or  improper  mixing,  giving  an  excess  of  matrix  in  one  place  and 
a   deficiency   in   another.     It   was   found   by   experiment   that 
mortars  made  with  coarse  sand  had  the  largest  volume  of  ap- 
parent voids. 

It  has  been  shown  elsewhere  that  if  dry  sand  be  moistened 
and  agitated,  the  bulk  of  the  sand  is  increased.  This  is  caused 
partially  by  the  imprisonment  of  air  bubbles  in  the  mass,  and 
if  a  measure  of  sand  so  treated  is  filled  with  water,  the  bubbles 
will  rise  to  the  surface  on  jarring  the  vessel.  Latent  voids  in 
mortar  are  due  to  a  similar  action,  and  hardened  mortars  con- 

1  Extrait  des  Annales  des  Fonts  et  Chaussees,  September,  1890. 


POROMTY  AND  PERMEABILITY  341 

taining  such  voids  refuse  to  absorb  water  to  replace  the  air 
bubbles,  at  least  for  a  long  time. 

481.  A  portion  of  the  water  used   in  mixing  mortar  enters 
into  chemical  combination  with  the  cement,  another  portion  is 
absorbed  by  the  sand  grains,  and  a  third  portion  goes  to  moisten 
the  sand.     The  quantity  absorbed  by  the  grains  depends  upon 
the  character  of  the  sand,  and  the  amount  required  to  moisten 
the  sand  depends  upon  the  superficial  area  of  the  grains  in  a 
given  volume,  being  greatest  for  fine  sands  and  least  for  coarse 
ones.     At    least  one  fourth    of    the    water    ordinarily    used    in 
mixing  neat  cement   is   given  off  later,  if  the  hardened   mor- 
tar  is   allowed   to   remain   in   dry  air.     The   water  required   to 
moisten   the   sand,   and   at   least  a  part  of  that  absorbed    by 
the  sand  grains,  also  dries  out,  leaving  voids  of  the  third  class 
mentioned. 

The  apparent  voids  may  be  reduced  to  a  very  small  per- 
centage by  care  in  the  proportions  and  preparation  of  the 
mortar.  The  latent  voids  may  amount  to  six  or  seven  per 
cent,  of  the  total  volume.  The  evaporation  of  water  may 
leave  from  six  to  eighteen  per  cent,  of  voids  in  the  mass. 

482.  The   conclusions   drawn   from   M.    Alexandre's   experi- 
ments are  briefly  as  follows:  The  porosity  varies  between  wide 
limits  according  to  the  fineness  of  the  sand  and  the  richness  of 
the  mortar.     It  may  be  as  low  as  thirteen  per  cent,  and  may 
exceed  thirty-one  per  cent. 

With  sand  of  the  same  degree  of  fineness,  the  porosity  di- 
minishes as  the  proportion  of  cement  in  the  mortar  increases. 

With  the  same  quantity  of  cement  per  volume  of  sand,  the 
porosity  increases  with  the  fineness  of  the  sand.  This  is  es- 
pecially marked  in  rich  mortars,  where  the  increase  in  porosity 
may  reach  50  to  100  per  cent.,  while  in  lean  mortars  the  use 
of  a  fine  sand  may  not  increase  the  percentage  of  voids  more 
than  20  per  cent. 

The  least  porous  mortars  are  those  rich  in  cement  and  made 
with  coarse  sand.  Mortars  made  with  fine  sand  are  relatively 
very  porous,  even  when,  made  rich  with  cement. 

Mortars  gaged  dry  are  more  porous  than  those  of  ordinary 
consistency,  and  mortars  gaged  wet  are  also  likely  to  be  more 
porous,  unless  the  manipulation  is  such  as  to  allow  the  excess 
water  to  rise  to  the  surface  of  the  mortar.. 


342  CEMENT  AND  CONCRETE 

483.  Permeability  —  The  degree  of  permeability  of   mortars 
is  a  more  important  property  than  the  porosity,  since  not  only 
does  it  affect  the  suitability  of  the  mortar  for   certain  uses, 
but  the  life  of  the  structure  may  depend  upon  the  difficulty 
with  which  water  may  percolate  the  mass. 

The  permeability  of  mortar  decreases  as  the  proportion  of 
cement  is  augmented,  and  in  the  case  of  concretes  the  per- 
meability diminishes  as  the  percentage  of  mortar  increases,  at 
least  to  the  point  where  the  latter  is  in  excess  of  the  voids  in 
the  stone. 

From  experiments  made  at  the  Thayer  School  of  Civil  En- 
gineering, Messrs.  J.  B.  Mclntyre  and  A.  L.  True  found  that  a 
five-inch  layer  of  concrete  containing  from  30  to  45  per  cent, 
of  one-to-one  Portland  cement  mortar,  and  some  of  the  speci- 
mens containing  40  to  45  per  cent,  of  one-to-two  mortar,  were 
impermeable  with  pressures  of  20  to  80  pounds  per  square 
inch,  maintained  for  two  hours. 

484.  Mortars  made  with  fine  sand  are  much  less  permeable 
than  those  made  with  coarse  sand.     This  difference  is  so  marked 
that  a  less  permeable  mortar  is  made  with  one  barrel  of  cement 
per  cubic  yard  of  fine  sand,  passing  a  sieve  having,  say,  fifty 
meshes  per  inch,  than  with  two  barrels  of  cement  per  cubic 
yard  of  very  coarse  sand  in  which  the  grains  are,  say,  one- 
tenth  inch  in  diameter.     Mortars  made  with  sands  composed 
of  a  mixture  of  grains  of  various  sizes  are  neither  very  porous 
nor  easily  permeated. 

Mortars  mixed  very  dry  or  very  wet  have  greater  permeabil- 
ity than  those  of  the  ordinary  consistency,  and  in  the  case  of 
concretes,  it  would  probably  be  found  that  a  deficiency  of 
water  would  result  in  a  much  more  permeable  mass  than  the 
use  of  what  might  be  considered  an  excess. 

All  of  the  above  conclusions  indicate  that  a  mortar  may  be 
quite  porous,  and  yet  so  long  as  the  voids  are  very  minute,  the 
percolation  of  water  through  it  will  be  slow.  This  is  especially 
shown  by  the  fact  that  mortars  of  coarse  sand,  not  porous, 
are  more  permeable  than  the  porous  mortars  of  fine  sand. 

485.  When   water   is   permitted   to    percolate    continuously 
through  a  mass  of  mortar,  the  interstices  gradually  become  filled, 
and  the  permeability  decreases  in  marked   degree.     M.   Alex- 
andre  found  that  a  volume  of  water  which  passed  a  certain 


WA  TER-PROOFING  .°>43 

mass  of  mortar  in  twenty  minutes  at  the  beginning  of  the  ex- 
periment, required  five  hours  to  percolate  the  mass  at  the  end 
of  a  month.  M.  R.  Feret  has  obtained  similar  results  in  making 
extensive  experiments l  on  the  subject  of  permeability,  and 
considers  that  fine  particles  of  cement  or  lime  are  carried  along 
by  the  water,  forming  efflorescence  at  the  surface  and  tending 
to  stop  the  flow. 

486.  The  Preparation  of  Water-Proof  Mortar  and  Concrete. 
-  To   enumerate   briefly   the   precautions   necessary   to   attain 

water-tightness  in  mortars  and  concretes,  it  may  be  said  that 
different  brands  of  cement  present  different  characteristics  in 
this  regard.  Fine  grinding  is  a  prime  requisite,  and  sand 
cement  or  silica  cement,  containing  as  it  does  very  fine  grains  of 
sand  intimately  mixed  with  cement  particles  of  extreme  fine- 
ness, is  admirably  adapted  to  such  uses. 

The  Sand  should,  if  possible,  be  composed  of  a  mixture  of 
grains  of  various  sizes,  because  such  a  mixture  gives  a  mortar 
not  only  little  permeable,  but  one  that  is  not  porous,  and  that 
has,  besides,  a  good  strength.  The  amount  of  cement  in  the 
mortar  should  be  in  excess  of  the  voids  in  the  sand,  not  less, 
in  general,  than  three  barrels  of  cement  per  cubic  yard  of  sand. 

In  concrete  the  volume  of  mortar  should  exceed  the  volume 
of  voids  in  the  aggregate,  and  to  obtain  this  result  without 
too  great  expense,  the  aggregate  should  be  so  selected  as  to  have 
a  minimum  of  voids.  Gravel  concrete  properly  proportioned 
may  be  made  water-tight  somewhat  more  easily  than  broken- 
stone  concrete,  but  a  mixture  of  gravel  and  broken  stone  will 
give  good  results  not  only  in  this  regard,  but  in  the  matter  of 
strength  as  well. 

487.  To  make  a  compact  mortar  for  use  where  the  facilities 
for   tamping   are   ordinarily   good,    the   consistency   should    be 
neither  very  wet  nor  very  dry.     When  the  mortar  is  struck 
with  the  back  of  a  shovel,  moisture  should  glisten  on  the  surface, 
but  in  a  pile  the  mortar  should  appear  but  little  moister  than 
fresh  earth.     This  is  the  consistency  which,  with  a  moderate 
amount   of   tamping,   gives   the   least   volume   of   mortar   with 
given  quantities  of  dry  materials.     In  places  difficult  of  access, 


1  "La  Capacit^  des  Mortier  Hydrauliques,"  Annales  des  Fonts  et  Chausstes, 
July.  1892. 


344  CEMENT  AND  CONCRETE 

or  in  the  preparation  of  concrete,  better  results  will  be  obtained 
with  a  mortar  somewhat  wetter  than  the  above,  since  large 
voids  will  be  less  likely  to  occur  in  the  more  plastic  mass.  In 
fact,  unless  the  supervision  is  very  close,  it  is  advisable  to  use 
a  rather  wet  mixture  in  preparing  concrete  where  water-tight- 
ness is  desired. 

488.  Washes.  —  The  application  of  certain  washes  to  the 
surfaces  of  walls  intended  to  be  water-proof,  and  the  introduc- 
tion of  foreign  materials  into  the  mortar  or  concrete  to  make 
it  less  permeable,  have  been  practiced  to  some  extent.  Alter- 
nate coatings  of  soap  and  alum  solutions  are  applied  with  a 
brush,  not  only  to  concrete,  but  to  brick  and  stone  masonry 
surfaces.  These  penetrate  the  pores  of  the  masonry,  forming 
insoluble  compounds  which  prevent  percolation.  Washes  of 
grout,  composed  of  cement,  or  of  cement  and  slaked  lime,  are 
used  for  a  similar  purpose. 

"Sylvester's  Process  for  Repelling  Moisture  from  External 
Walls"  consists  in  applying  first  a  solution  of  three  quarters 
of  a  pound  of  soap  to  one  gallon  of  water,  followed,  after  twenty- 
four  hours,  by  the  application  of  a  solution  containing  two 
ounces  of  alum  per  gallon  of  water.  Both  solutions  are  applied 
with  a  brush,  the  soap  solution  boiling  hot,  and  the  alum  so- 
lution at  60°  to  70°  Fahr.  The  applications  are  alternated, 
with  twenty-four  hours  intervening  each  time.  Experiments  at 
the  Croton  Reservoir  l  indicated  that  four  coats  of  each  wash 
were  required  to  render  brickwork  impervious  to  a  head  of  forty 
feet  of  water  and  the  cost  of  the  four  double  applications  was 
about  ten  cents  a  square  foot. 

In  Reservoir  Number  Two  of  the  Pennsylvania  Water  Co., 
two  washes  of  each  solution  were  used  on  the  walls  at  a  cost 
for  materials  and  labor  of  twenty-three  cents  per  hundred 
square  feet,  and  the  results  were  said  to  be  good. 

A  modified  recipe  for  such  a  wash  in  which  but  one  solution 
is  made  is  given  as  follows:2  A  stock  solution  is  prepared  of 
one  pound  lye,  five  pounds  powdered  alum,  dissolved  in  two 
quarts  water.  One  pint  of  the  stock  is  used  to  a  pail  of  water 
in  which  ten  pounds  Portland  cement  has  been  well  mixed. 


1  Trans.  A.  S.  C.  E.,  Vol.  i,  p.  203. 

2  J.  H.  G.  Wolf,  Engineering  News,  June  30,  1904. 


WATER-PROOFING  345 

489.  In  a  few  cases  the  use  of   alum  and  soap  solutions  in 
the  body  of  the  mortar  has  been  tried  with  apparently  success- 
ful results.     Mr.  Edward  Cunningham,1  in  making  experiments 
on  water-proof  concrete  vessels,  used  powdered  alum  equal  to 
one  per  cent,  of  the  combined  weight  of  the  sand  and  cement, 
mixing  this  with  the  dry  ingredients.     To  the  water  used  in 
mixing,  one  per  cent,  of  yellow  soap  was  added.     The  results 
were  said  to  be  very  satisfactory.     In  the  above  proportions, 
however,   the   amount  of   alum   is   made   to   depend   upon    the 
amount  of  cement  and  sand  used,  while  the  soap  added  depends 
upon  the  amount  of  water,  whereas  the  soap  should  bear  a  de- 
finite ratio  to  the  alum. 

In  experiments  with  mortar  composed  of  one  part  cement 
to  two  and  one-half  parts  of  bituminous  ash,  Prof.  W.  K.  Hatt 2 
found  that  the  alum  and  soap  mixed  with  the  mortar  at  the 
time  of  gaging  increased  the  strength  and  hardness  of  the  ash 
mortar  about  fifty  per  cent.,  and  diminished  the  absorption  by 
the  same  percentage.  One  half  of  the  water  used  for  gaging 
was  a  five  per  cent,  solution  of  ground  alum,  the  other  half 
being  a  seven  per  cent,  solution  of  soap.  The  alum  solution 
was  used  first  and  the  gaging  completed  with  the  soap  solution. 

Mr.  W.  C.  Hawley  8  employed  a  stock  solution  of  two  pounds 
caustic  potash,  five  pounds  powdered  alum,  and  ten  quarts 
water,  and  used  in  the  finishing  coat  three  quarts  of  this  solu- 
tion in  each  batch  of  mortar  containing  two  bags  of  cement. 
The  mortar  was  mixed  with  two  volumes  of  sand  to  one  of  ce- 
ment and  covered  forty-eight  square  feet  to  a  depth  of  about 
one-half  inch.  The  extra  cost  for  materials  and  preparing  so- 
lution was  only  about  nine  and  a  half  cents  per  hundred  square 
feet.  With  less  than  two  parts  sand  to  one  cement,  it  was 
found  the  finishing  mortar  checked  in  setting.  It  was  also 
found  that  any  organic  matter  in  the  sand  was  softened  by  the 
potash,  and  an  excess  of  potash  caused  checking,  although  an 
excess  of  alum  had  no  deleterious  effect. 

490.  Use  of  Lime,  etc.  —  The  introduction  of  slaked  lime  in 
mortars   designed  to  be  water-proof  is  suggested  by  the  fact 


1  Trans.  A.  S.  C.  E.,  Vol.  li,  p.  128. 
8  Trans.  A.  S.  C.  E.,  Vol.  li,  p.  129. 
1  Journal  New  England  Water- Works  Association,  1904. 


346  CEMENT  AND  CONCRETE 

that  the  permeability  of  mortar  diminishes  if  water  is  allowed 
to  percolate  it  for  some  time,  the  theory  being  that  fine  par- 
ticles of  cement  and  lime  are  dislodged  by  the  passage  of  the 
water  to  form  a  deposit  at  or  near  the  surface,  and  check  the 
flow.  This  suggestion,  however,  needs  experimental  confirma- 
tion, since  it  seems  quite  possible  that  the  introduction  of  a 
substance  containing  such  a  large  proportion  of  water  as  does 
slaked  lime,  may  increase  the  percentage  of  voids  in  the  mor- 
tar, if  not  the  permeability. 

The  use  of  pulverized  clay  and  pozzolanic  materials  for  a 
similar  purpose  has  been  suggested.  It  has  already  been  shown 
that  moderate  doses  of  clay  have  no  deleterious  effect  on  the 
strength  of  mortars  for  ordinary  exposures.  The  action  of  the 
pozzolanic  substances  has  been  found  by  Dr.  Michaelis  and 
M.  Feret  to  be  not  mechanical  alone,  but  chemical,  and  the 
effect  on  the  strength  of  the  resulting  mortar  depends  upon  the 
exposure  to  which  it  is  subjected,  such  admixtures  being  dele- 
terious for  mortars  hardened  in  air. 

491.  Efflorescence.  —  The  white    deposit    sometimes   formed 
at  the  surface  of  brick  and  masonry  walls  is  usually  due  to  the 
filtration  of  water  through  the  mortar,  dissolving  out  salts  of 
potash,  soda,  etc.,  and  depositing  these  salts  on  the  surface  by 
evaporation  or  by  the  formation  of   sodic  carbonate.     The  ab- 
sorption of  water  from  the  atmosphere  may  also  account  for 
this  deposit  in  some  degree,  especially  near  the  sea.     The  same 
term  is  applied  to  a  more  harmful  deposit,  sulphate  of  calcium, 
which  may  be  supplied  by  the  filtrating  water  or  may  come 
from  the  cement,  either  from  the  addition  of  gypsum  or  from 
the  fuel  used  in  burning.     The  crystallization  of  this  salt  in  the 
pores  of  the  masonry  at  the  surface  may  cause  disintegration. 

On  the  other  hand  efflorescence  may  be  quite  harmless,  as 
when  it  is  formed  by  washing  out  from  the  mortar  an  excess  of 
hydrate  of  lime.  A  portion  of  the  latter  may  then  be  changed 
to  carbonate  of  lime  near  the  surface  of  the  wall  and  actually 
stop  up  the  pores  or  voids,  and  prevent  further  filtration. 

492.  The  discoloration  of    brickwork  and  fine  masonry  by 
efflorescence  is  sometimes  serious.     To  ameliorate  these  condi- 
tions, the  use  of  water-proof  mortars,  and  careful  pointing  of 
the  work,  are  precautions  to  be  recommended.     General  Gill- 
more,  in  "  Limes,  Hydraulic  Cements  and  Mortars/'  suggests 


EFFLORESCENCE  347 

the  use  of  about  ten  pounds  of  animal  fat  to  one  hundred  pounds 
of  lime  and  three  hundred  pounds  of  cement;  the  object  of  the 
fat  being  to  saponify  the  alkaline  substance,  the  lime  in  form 
of  paste  serving  only  as  a  vehicle  for  the  fat.  A  more  practical 
method,  however,  would  seem  to  be  the  application  of  soap 
and  alum  washes  on  the  surface,  or  the  use  of  soap  and  alum 
in  the  preparation  of  the  mortar  to  be  used  near  the  face  of  the 
wall,  and  especially  for  pointing.  The  remedy  to  be  adopted, 
however,  will  depend  upon  the  cause  of  the  efflorescence. 

493.  Pointing  Mortar.  —  Pointing  serves  the  double  purpose 
of  making  the  joint  practically  water-tight  at  the  edges,  and  giv- 
ing a  finish  to  the  face  of  the  wall.     If  the  edge  of  the  joint  is 
not  well  filled,  moisture  collects  there  either  from  the  face  or 
from  seepage   through   the   wall.     Subsequent  freezing  or  the 
crystallization  of  certain  salts  may  spall  the  stones  or  loosen 
them  from  their  bed. 

In  laying  cut-stone  masonry,  the  joints  should  be  raked  out 
for  about  two  inches  back  from  the  face  to  be  pointed. 
Pointing  mortar  should  be  prepared  from  fine  sand  and  the 
best  Portland  cement.  The  proportion  of  sand  should  not 
exceed  two  parts  by  weight  to  one  cement,  and  in  the  highest 
class  work,  equal  parts  of  cement  and  sand  are  sometimes 
used.  No  advantage  is  gained,  however,  by  using  a  mortar 
richer  in  cement  than  the  one  last  mentioned.  The  use  of  fine 
sand  and  rich  mortars  are  specified  not  only  because  such  mor- 
tars are  practically  water-tight,  but  because  they  take  a  fine 
finish. 

494.  The  tools  required  for  pointing  are  a  bent  iron  to  rake 
out  the  joints  (though  this  should  be  partially  done  while  the 
mortar  is  green),  a  mortar  board  and  small  trowel,  a  calking 
iron  and  wooden  mallet,  a  brush  for  moistening  the  joint,  and 
one  or  more  beading  tools.     After  raking  out  the  joint  it  is 
moistened  by  the  brush,  and  the  mortar,  which  is  mixed  quite 
dry.  is  filled  in  with  the  trowel.     When  enough  mortar  is  in 
place  to  fill  half  the  depth  of  the  joint,  it  is  tamped  with  the 
calking  iron  and  mallet  much  as  a  ship's    seam  is  calked  with 
oakum.     The  joint  is  then  filled  to  the  face,  and  again  tamped. 
The  bead  is  then  formed  by  running  the  beading  iron  back 
and  forth  over  the  joint.     This  beading  iron  is  of  steel  with  the 
handle  parallel  to,  but  some  two  or  three  inches  out  from,  the 


348  CEMENT  AND  CONCRETE 

line  of  the  blade  forming  the  bead.  The  blade  is  three  to  five 
inches  long  and  " hollow  ground"  or  finished  with  a  smooth 
concave  surface.  Only  such  a  length  of  joint  is  pointed  at  one 
operation  as  may  be  quickly  carried  to  completion.  The  wall 
must  be  kept  moist  for  some  time  after  the  pointing  is  done, 
and  it  should  be  protected  from  the  direct  rays  of  the  sun,  as 
fine  cracks  are  very  likely  to  appear  in  this  rich,  finely  finished 
mortar.  If  possible,  pointing  should  be  done  in  moderate 
weather  and  must  be  entirely  suspended  in  temperatures  ap- 
proaching the  freezing  point. 

495.  Cements  in  Sea  Water.  —  The  theory  of  the  action  of 
sea  water  upon  cements  is  not  fully  understood.     It  is  known 
that  some  cement  structures  exposed  to  the  worst  conditions 
have  given  most  satisfactory  results,  while  others  have  failed 
in  greater  or  less  degree.     It  may  be  said  at  once,  however, 
that   many   of   the   most   eminent   and   conservative   engineers 
consider  that  the  failures  that  have  occurred  in  the  use  of  Port- 
land cement  in  sea  water  are  due  to  improper  specifications, 
proportions   and   manipulation,   rather   than  to   any  defect  in 
Portland  cements  as  a  class. 

496.  It  is  thought  the  following  represents,  in  the  main,  the 
most  generally  accepted  theory  of  the  chemical  action.     In  the 
setting  of  cements  that  are  rich  .in  lime,  the  whole  of  the  lime 
is  not  engaged   in   stable  compounds,  and  when  placed  in  the 
sea  the  sulphate  of  magnesia  of  the  sea  water  is  able  to  com- 
bine with  the  lime,  forming  calcic  sulphate,  the  magnesia  being 
precipitated.     The  discovery  of  magnesia  in  decomposed  mor- 
tars led,  at  first,  to  the  supposition  that  the  cause  of  failure 
was  the  presence  of  magnesia  in  the   cement  when  used.     If 
the  water  level  about  the  structure  changes  frequently,  as  is 
usual,  or  if  the  wall  is  at  times  subjected  to  a  greater  head  on 
one  side  than  on  the  other  as  in  tide  docks,  the  percolation  of 
water  through  the  wall  is  stimulated,  and  the  sulphate  of  lime 
may  then  be  washed  out  if  the  mortar  is  quite  pervious,  and 
more  will  be  formed  from  a  fresh  supply  of  sea  water  attacking 
the  lime  of  the  cement,  until  the  latter  is  destroyed.     If,  how- 
ever, the  sulphate  of  lime  is  not  washed  out,  it  may  crystallize 
and  thus  cause  swelling  of  the  mortar. 

497.  It  would   appear  from  the   above   that    for  successful 
use  in  sea  water  the  hydraulic  index  of  the  cement  should  be 


ACTION  OF  SEA    WATER  349 

high;  that  is,  that  the  lime  should  be  comparatively  low  in  or- 
der that  the  lime  compounds  may  be  more  stable.  For  this 
reason  it  is  not  impossible  that  some  of  our  natural  cements, 
which  are  so  much  more  nearly  uniform  than  the  Roman  ce- 
ments of  Europe  that  have  been  condemned  for  this  reason, 
may  give  fairly  good  results  in  sea  water.  The  fact  that  the 
mortars  of  natural  cement  are  more  permeable  than  those  of 
Portland,  is,  however,  a  serious  defect. 

Following  a  similar  reasoning,  Dr.  Win.  Michaelis  has  ad- 
vanced the  theory  that  if  trass,  or  other  pozzolanas  of  proper 
composition,  be  mixed  with  Portland  cement  subsequent  to 
the  burning,  the  hydrate  of  lime  which  separates  from  the  ce- 
ment in  hardening  will  at  once  combine  with  the  pozzolanas, 
forming  a  stable  compound.  This  view,  however,  has  been 
vigorously  opposed  by  the  Society  of  German  Portland  Cement 
Manufacturers,  as  well  as  by  many  engineers,  especially  of 
France,  and  the  discussion  is  not  yet  at  an  end. 

M.  Candlot l  says  that,  from  the  experiments  of  various  en- 
gineers, "we  have  arrived  at  this  conclusion,  that  the  only 
remedy  to  adopt  against  decomposition  is  to  prevent  the  sea 
water  from  penetrating  the  mortar.  We  are  led  thus  to  dis- 
miss the  chemical  reactions  of  sea  water  on  mortars  and  to 
consider  their  action  from  a  purely  physical  standpoint." 

498.  To  resist  the  attacks  of  sea  water  the  mortar  should  not 
only  be  impervious,  but  also  as  little  porous  as  possible.  The 
cement  should  be  finely  ground  and  should  not  contain  free 
lime.  The  content  of  magnesia  and  of  sulphuric  anhydride 
should  be  as  low  as  possible,  the  latter  not  exceeding  one  and 
five-tenths  per  cent.  The  proportion  of  lime  should  not  be 
too  high,  and  above  all,  special  pains  should  be  taken  with  the 
manufacture  to  insure  proper  comminution  and  mixing  of  the 
raw  materials,  and  uniform  burning.  The  addition  of  sulphate 
of  lime  to  regulate  the  setting  is  believed  to  be  injurious  for 
cements  to  be  used  in  sea  water;  even  two  or  three  per  cent, 
is  said  to  cause  rapid  disintegration,  and  in  the  specifications 
for  recent  extensive  works  in  dock  construction,  the  addition 
of  gypsum  or  other  foreign  matter  was  entirely  prohibited. 


"Le  Cimcnt,"  September,  1896,  quoted  by  F.  H.  Lewis,  M.  Am.  Soc. 
C.  E.     Trans.  A.  S.  C.  E.,  Vol.  xxxvii,  p.  523. 


350  CEMENT  AND  CONCRETE 

Although  slag  cements  have  given  good  results  in  the  sea 
for  a  short  time,  it  is  considered  that  they  will  not,  in  general, 
resist  the  action  of  sea  water  for  long  periods. 

499.  Sand  or  aggregate  containing  argillaceous  or  soft   cal- 
careous matter  should  be  avoided  for  works  in  the  sea.     Two 
instances  of  failure  of  sea  walls  in  which  shells  were  used  as  the 
aggregate  are  mentioned  by  Col.  Wm.  M.  Black,1  and  although 
the  failures  are  not  definitely  traced  to  the  calcareous  matter  in 
the  concrete,  the  fact  that  experiments  have  shown  that  cal- 
careous sands  do  not  withstand  the  action  of  sea  water,  makes 
it  probable  that  this  was  an  important  cause  of  the  failure. 

Fine  sands  that  give  porous  mortars,  though  not  easily  per- 
meable, are  to  be  strictly  avoided.  Coarse  sands  giving  per- 
meable, though  not  porous,  mortars  are  better,  but  still  leave 
much  to  be  desired  as  to  immunity  from  decomposition.  The 
best  sands  are  those  containing  various  grades  of  sizes  of  par- 
ticles from  coarse  to  fine,  as  mortars  made  with  such  sands  are 
not  only  compact,  but  practically  impermeable. 

500.  Since  the  mortar  and  concrete  should  be  made  as  com- 
pact as  possible,  the  precautions  mentioned  under  the  head  of 
water-proof  mortar  and  concrete  should  be  taken  in  the  prep- 
aration of  mortars  and  concretes  for  use  in  the  sea.     That  is, 
the  proportion  of  cement  should  exceed  the  voids  in  the  sand 
and  the  mortar  should  exceed  the  voids  in  the  aggregate. 

M.  Alexandre  has  found  that  the  mortars  mixed  to  the  or- 
dinary consistency  are  attacked  least  by  sea  water.  When 
specimens  are  merely  immersed  in  the  water,  those  mixed  dry 
suffer  the  most,  but  some  tests  indicate  that  if  mortars  are 
submitted  to  the  filtration  of  water  soon  after  made,  those 
mixed  wet  are  most  easily  decomposed.  As  to  whether  fresh 
or  salt  wafer  should  be  employed  in  mixing  mortars  to  be  used 
in  sea  water,  although  Mr.  Eliot  C.  Clarke,  M.  Paul  Alexandre 
and  many  others  have  investigated  this  subject,  the  conclusions 
are  not  definite  and  it  is  probable  that  either  may  be  used  as 
convenient. 


Trans.  A.  S.  C.  E.,  Vol.  xxx,  p.  601. 


PART  IV 

USE    OF   MORTAR   AND    CONCRETE 
CHAPTER  XVIII 

CONCRETE :     DEPOSITION 

501.  Concrete  may  be  molded  into  blocks  which  are  allowed 
to  set  and  then  are  transported  to  the  structure  and  laid  as 
blocks  of  stone.  This  is  the  block  system  of  construction.  The 
adaptability  of  concrete  to  being  built  in  place,  however,  is 
one  of  its  chief  merits,  and  consequently  the  monolithic  method 
of  construction  is  far  more  common  Since  it  has  been  found 
that  expansion  and  contraction,  due  to  changes  in  temperature, 
affect  concrete  walls  as  they  do  any  other  walls  of  masonry, 
it  has  become  customary  to  mold  the  concrete  in  sections,  usu- 
ally alternate  sections  of  equal  size  and  shape  being  built  first, 
and  the  omitted  sections  built  in  later.  This  method  of  con- 
structing a  long  wall  is  also  called  monolithic,  since  the  blocks 
are  of  large  size  and  are  built  in  place. 

502.  When  concrete  is  deposited    either  in  air  or   in  water, 
molds  must  be  provided  to  keep  the  mass  in  the  desired  shape 
until  it  has  lost  its  plasticity  and  acquired  sufficient  strength 
to  stand  alone.     In  foundations,  the  earth  at  the  sides  of  the 
excavation  may  supply  the  place  of  a  mold,  and  sometimes 
the  mold  forms  a  part  of  the  permanent  structure,  as  in  the 
case  of  masonry  piers  with  concrete  hearting,  and  in  steel  cylin- 
der piers  filled  with  concrete. 

ART.  62.     TIMBER  FORMS  OR  MOLDS 

503.  The  construction,  placing  and  removal  of    forms  fre- 
quently represent  a  considerable  percentage,  from  five  to  thirty 
per  cent.,  of  the  total  cost  of  the  concrete,  and  it  is  therefore 
evident  that  an  improper  design  may  result  in  a  considerable 
waste  of  money,  as  well  as  in  marring  the  appearance  of  the 

351 


352  CEMENT  AND  CONCRETE 

work.  The  character  of  the  form  will  of  course  depend  on  the 
character  of  the  work;  in  the  construction  of  a  large  number 
of  small  blocks  of  the  same  shape,  where  one  mold  may  be  used 
over  and  over,  the  thickness  of  the  pieces  should  not  be  stinted, 
and  the  ease  of  knocking  down  the  mold  should  be  carefully 
considered.  When  a  form  can  be  used  but  once,  the  size  of 
pieces  should  be  no  larger  than  necessary  to  give  the  requisite 
stiffness,  and  the  ease  of  first  construction  is  a  main  considera- 
tion. Forms  should  be  left  in  place  forty-eight  hours  to  allow 
the  concrete  to  set,  and  in  the  case  of  arches  and  beams  a 
much  longer  time  is  necessary,  so  that  the  concrete  may  assume 
considerable  strength  before  it  is  called  upon  to  support  its 
weight. 

504.  Sheathing.  —  Forms   for   massive    walls    of    monolithic 
construction  usually  have  vertical  posts,  with  iron  ties  across, 
or  braced   by   battered   posts   outside.     The   sheathing   planks 
are  then  placed  horizontal.     In  a  few  cases  horizontal   wales 
have  been  placed  within  the  posts  and  vertical  sheathing  laid 
against  the  wales. 

The  strength  of  the  sheathing  must  be  sufficient  to  stand 
the  pressure  transmitted  to  it  through  the  concrete  when  the 
rammer  is  used  close  to  the  face  of  the  mold.  The  concrete  is 
seldom  built  up  fast  enough  to  bring  upon  the  sheathing  a  great 
head  of  fluid  pressure,  but  the  ramming  brings  a  heavy  local 
pressure  upon  it.  If  supported  at  intervals  of  four  feet,  two- 
inch  lumber  dressed  to  one  and  three-quarters  inches  thick  is 
usually  sufficient;  for  spans  of  more  than  5  feet,  2  }  inch  lum- 
ber is  required  to  make  a  perfect  face.  Boards  seven-eighths 
inch  thick  are  suitable  only  when  supports  are  not  more  than 
about  2  feet  apart.  In  placing  concrete  in  molds  under  water 
there  is  more  danger  of  bursting  the  mold  by  the  weight  of 
semi-fluid  concrete,  and  if  the  work  is  .to  be  built  up  rapidly, 
this  must  be  guarded  against  by  sufficient  bracing. 

505.  For  exposed  faces,  the  duty  to    be  performed  by  the 
lagging  includes  leaving  as  smooth  a  finish  as  possible  on  the 
concrete  after  the  removal  of  the  forms.     If  green  lumber  is 
employed,  the  boards  may  shrink  before  use,  leaving  openings 
between  the  sheathing  that  will  show  plainly  on  the  face  of  the 
work.     A   slight  tendency  of   this   kind   may   be   checked     by 
keeping  the  boards  well  wet   with  a  hose  until  the  concrete  is 


TIMBER  FORMS  353 

placed.  On  the  other  hand,  thoroughly  seasoned  lumber  will 
swell  when  the  concrete  is  placed;  to  obviate  this  difficulty  the 
lower  edge  of  each  sheathing  plank  may  be  beveled  on  the  outer 
edge;  the  thin  edge  on  the  inside  will  then  crush  when  the 
planks  swell. 

The  use  of  tongue  and  grooved  lagging  has  been  tried,  but 
is  not  usually  satisfactory,  as  there  is  no  opportunity  to  expand, 
and  the  planks  are  particularly  hard  to  place  a  second  time. 
To  give  a  good  face  in  work  under  water,  however,  tongue  and 
groove  sheathing  will  assist  in  preventing  washing  of  the  cement. 
Yellow  pine  lumber  is  found  to  be  excellent  for  sheathing;  on 
account  of  the  large  amount  of  pitch  contained,  it  absorbs 
water  slowly  and  holds  its  shape.  For  a  similar  reason,  fir 
timber  would  be  suitable. 

In  order  that  the  face  of  the  mold  shall  be  perfectly  smooth, 
it  is  necessary  to  size  and  dress  the  plank  on  at  least  one  side 
and  two  edges. 

As  it  is  almost  impossible  to  avoid  having  some  line  of  de- 
marcation shown  in  the  concrete  at  the  joints  of  the  sheathing 
planks,  care  should  be  taken  that  the  lagging  is  of  uniform 
width  throughout,  and  laid  horizontal  so  that  consecutive  sec- 
tions show  the  joint  continuous.  The  sheathing  may  be  placed 
for  the  entire  form  before  concreting  is  commenced,  or  the 
plank  may  be  raised  on  the  posts  as  the  work  advances.  The 
former  method  will  usually  give  the  neater  appearance,  but  is 
too  expensive  for  high  walls. 

506.  Lining.  —  The  appearance  of  the  finished  concrete  is 
much  improved,  and  the  labor  of  preparing  the  forms  probably 
not  increased,  since  less  care  may  be  taken  in  surfacing,  by 
lining  the  mold  with  thin  sheet  iron.  Iron  of  number  twenty 
gauge  (.035  inch  thick,  1.42  pounds  per  square  foot)  has  been 
used  for  this  purpose,  but  where  the  same  lining  is  used  several 
times,  a  heavier  iron  is  preferable.  The  joining  of  one  sheet  of 
lining  to  another  may  present  greater  difficulties  than  the  join- 
ing of  planks,  but  joints  will  occur  less  frequently. 

In  the  construction  of  the  Marquette  Breakwater,  Mr. 
Clarence  Coleman,  Asst.  Engineer,  used  sheet  steel  one  eighth 
of  an  inch  thick  for  lining  molds  for  building  monolithic  blocks. 
Concerning  the  use  of  the  steel,  Mr.  Coleman  says:1  "Very 


Report  Chief  of  Engineers,  V.  S.  A.,  1898,  p.  2254. 


354  CEMENT  AND  CONCRETE 

smooth  surfaces  were  produced  on  the  slopes  of  the  concrete 
and  the  work  of  the  molders  was  greatly  facilitated  on  account 
of  the  comparative  ease  with  which  the  concrete  was  compacted 
under  the  slope  pieces  of  the  molds.  The  steel  effectually  pre- 
vented the  aggressive  friction  of  the  sharp  particles  of  broken 
stone  on  the  wooden  surfaces  of  the  molds,  thus  increasing  the 
life  of  the  molds  and  decreasing  the  cost  of  molding  the  con- 
crete." 

507.  Oiling  the  Forms.  —  Oiling  or  greasing  the  face  of   the 
mold,  in  order  that  the  latter  may  be  removed  without  detach- 
ing particles  from  the  concrete  face,  is  usually  advisable.      Soap, 
crude  oil,  linseed  oil,  bacon  fat,  are  some  of  the  materials  that 
have  been  used  for  this  purpose;  the  first  mentioned  probably 
gives  the  best  results,  and  if  not  applied  too  freely  will  have  no 
injurious  effect  upon  either  the  finish  or  strength  of  the  work. 
Applying  shellac  to  the  molds  improves  the  appearance  of  the 
concrete   surface.     When   the   forms   are  lined   with   steel,    the 
adhesion  of  the  concrete  to  the  lining  is  more  difficult  to  over- 
come.    In  this  case  the  ordinary  oils  are  not  entirely  success- 
ful,   but   fat   salt   pork   has    been   found   to    give   satisfactory 
results. 

508.  Joints  and  Corners.  —  If  desired,  triangular  strips  may 
be  nailed  to  the  inside  of  the  forms  in  such  a  way  as  to  block 
off  the  face  to  represent  stone  masonry,  and  in  this  way  the 
marks  of  joints  between  planks  or  between  strips  of  lining  may 
be  avoided.     Square  corners  should  not  be  allowed  on  exterior 
angles,  as  it  is  difficult  to  so  tamp  the  concrete  as  to  make  the 
corner  perfect,  and  they  are  so  likely  to  be  chipped  off.     Tri- 
angular strips  or  moldings  should  be  tacked  along  the  corners 
of  the  mold  as  a  fillet  to  cut  off  the  corner  by  a  plane  making 
equal  angles  with  the  adjacent  faces.     This  plane  may  be  from 
one  inch  to  two  inches  wide. 

To  form  water  drips  on  projecting  ledges,  such  as  door  caps 
and  sills,  abutment  copings,  etc.,  a  small  half-round  should  be 
nailed  to  the  upper  surface  of  the  mold  a  short  distance  back 
from  the  projecting  face.  This  leaves  a  ridge  at  the  edge  of 
the  under  side  of  projection  so  that  the  water  must  drip  from 
the  edge,  and  not  follow  back  to  the  main  wall  face. 

509.  POSTS  AND   BRACES.  —  The  sizes   of   posts  and  braces 
must  be  such  as  to  make  a  practically  unyielding  support  to 


TIMBER  FORMS  355 

the  sheathing.  With  one  and  three-quarters  inch  lagging,  posts 
may  be  four  feet  apart;  if  five  feet  four  inches  apart  (three  to 
each  sixteen  foot  length),  some  yielding  of  the  sheathing  may 
be  expected  if  it  is  less  than  two  and  three  quarter  inches. 
If  sheathing  is  four  inches  thick,  the  distance  between  posts 
may  be  six  or  seven  feet. 

Fir,  yellow  pine,  and  Norway  pine  are  suitable  for  posts. 
Three-inch  by  eight-inch  is  an  ordinary  size,  and  a  post  of 
these  dimensions  should  be  supported,  either  by  ties  or  braces, 
at  intervals  of  four  to  six  feet.  Where  the  posts  are  four  inches 
by  ten  inches,  supports  may  be  six  to  eight  feet  centers,  while 
with  six-inch  by  twelve-inch  posts,  the  distance  between  cen- 
ters of  supports  may  be  eight  to  ten  feet.  Posts  should  be 
sized  arid  dressed  on  the  side  which  is  to  receive  the  sheathing, 
in  order  that  the  alignment  may  be  perfect. 

510.  Methods  of   Bracing.  —  The   general  plan  of  the  mold 
may  vary  according  to  conditions,  the  following  methods  hav- 
ing been  employed  on  heavy  work  to  support  the  vertical  posts: 
1st,  With  outside  inclined  braces,  leaving  the  interior  of  the 
mold   unobstructed.     2d,   Tie   rods  across   the  interior  of  the 
mold  connecting  opposite  posts  at  frequent  intervals.     3d,  Each 
post  trussed  vertically  and  tied  across  at  top  and  bottom  only. 
4th,  Horizontal  trussed  wales  outside  of  posts,  spaced  four  to 
five  feet  apart  in  the  vertical  and  tied  across  at  the  ends. 

511.  Inclined  Braces.  —  The  sizes  of  inclined  braces  depend 
on  their  lengths,  the  inclination  to  the  vertical,  and  the  amount 
of  shoring  used.     An  approximate  rule  for  the  size  of  braces 
under   usual    conditions    and    using   ordinary   dimension   stuff, 
not  boards,  is  that  the  number  of  square  inches  area  of  cross- 
section  of  brace  should  equal  length  of  span  in  feet.     If  thin 
planks  are  employed,  they  should  be  in  pairs,  one  on  either 
side  of  the  vertical  post,  and  made  to  act  together  by  cross- 
pieces  nailed  to  the  two  planks. 

The  aim  should  be  to  make  the  whole  form  practically  un- 
yielding under  the  action  of  the  tampers,  as  it  has  been  found 
that  this  action  is  usually  more  severe  than  the  mere  pressure 
of  the  concrete  in  a  semi-liquid  condition.  The  sizes  of  pieces 
cannot,  therefore,  be  accurately  computed,  but  the  above  sizes 
are  derived  from  the  generafe-result  of  experience  as  to  what 
has  proved  satisfactory. 


356  CEMENT  AND  CONCRETE 

The  advantage  of  the  form  of  construction  just  described  is 
that  the  interior  of  the  mold  is  left  entirely  unobstructed.  On 
high  walls,  however,  the  amount  of  timber  required  for  braces 
is  excessive,  and  the  braces  may  be  almost  as  objectionable  as 
tie  rods,  since  the  former  prevent  the  laying  of  tracks  along 
the  side  of  the  form. 

512.  Tie  Rods.  —  When  the  vertical  posts  are  supported  by 
tie  rods  across  the  mold  and  the  wall  is  thin,  it  may  be  possible 
in  removing  the  mold  to  withdraw  the  bolts  or  rods  if  they 
have  been  thoroughly  greased  or  wrapped  with  stiff  paper  be- 
fore the  concrete  is  placed.     If  it  is  designed  to  leave  the  rods 
in  the  concrete,  they  should  be  provided  with  sleave  nuts  near 
the  end,  which,  when  unscrewed,  will  leave  the  end  of   the  rod 
within  the  concrete  mass  not  less  than  two  inches  from  the  face. 
The  hole  left  by  the  nut  should  be  carefully  filled  with  mortar 
after  the  mold  is  removed. 

With  vertical  posts  four  feet  apart,  this  method  of  support 
is  objectionable,  as  it  leaves  a  network  of  ties  within  the  forms 
interfering  seriously  with  the  operation  of  a  skip  and  with  the 
ramming.  It  is  not  necessary,  however,  to  place  all  of  the  tie 
rods  to  the  top  of  the  mold  before  beginning  the  concreting, 
as  it  is  sufficient  to  keep  one  or  two  rods  in  place  above  the 
plane  where  tamping  is  being  done, 

A  modification  of  this  method  is  to  use  wires  of  large  diam- 
eter with  an  eye  at  the  end  just  inside  the  finished  face  of 
the  concrete.  A  short  bolt,  with  hook  at  one  end  and  threaded 
at  the  other,  passes  through  the  post,  hooks  into  the  eye  of  the 
wire,  and  is  tightened  by  a  nut  on  the  threaded  end  outside 
the  post.  After  removing  the  nut,  the  rod  is  unhooked  and 
the  hole  in  the  face  filled  with  mortar,  the  wire  remaining  in 
the  concrete. 

513.  Trussed  Posts.  —  The  third  method  of   support,  where 
the  posts  are  trussed  and  provided  with    heavy  tie  rods  at  the 
top,  and  held  at  the  bottom  either  by  tie  rods  or  some  other 
means,  seems  to  have  fewer  objections  than  the  methods  just 
described.     Less  timber  will  usually  be  required  to  build  this 
form  than  for  that  where  inclined  braces  are  used,   and  the 
obstruction  to  operations  will  usually  be  less  than  with  either 
of  the  other  styles.     This  mold  is  also  very  readily  taken  down, 
though  the  posts  are  heavier  and  more  difficult  to  handle. 


TIMBER  FORMS  357 

To  secure  the  bottoms  of  the  posts,  they  may  be  set  in  the 
ground,  or  rest  against  sills  braced  to  some  other  portion  of 
the  structure,  or  to  piles.  A  suitable  support  may  also  be 
obtained  by  dumping  a  mass  of  concrete  around  the  bottom 
of  each  post  and  allowing  it  to  set.  Forms  erected  on  rock 
may  have  the  posts  rest  against  blocks  bolted  to  the  rock. 

514.  Trussed  Wales.  —  The  fourth  method  of  supporting  the 
posts  is  particularly  applicable  where  the  work  is  divided  into 
blocks  of  moderate  size  in  horizontal  cross-section,  say  twenty 
feet  square.  In  longer  lengths  the  horizontal  trussed  wales 
become  rather  heavy  for  convenient  handling.  Within  these 
limits,  however,  this  is  an  excellent  form.  In  the  construction 
of  Lock  No.  2  between  Minneapolis  and  St.  Paul,1  a  form  of 
this  kind  was  used  for  blocks  about  twelve  by  fifteen  feet  at  the 
bottom.  The  sheathing  was  one  and  three-quarters  inches, 
lined  with  No.  20  galvanized  iron.  Verticals  were  four  by 
twelve,  spaced  about  two  feet  centers.  The  trussed  wales  were 
twelve  by  twelve  inch,  trussed  with  one  and  one-quarter  inch 
rod,  the  king-post  being  of  twelve  by  twelve,  inch  about  two 
and  one-half  feet  long,  making  depth  of  truss  three  and  one- 
half  feet.  The  ends  of  opposite  wales  were  connected  by  one 
and  one-quarter  inch  rod  passing  outside  of  the  sheathing. 
Each  pair  of  the  longitudinal  wales  was  just  above  the  corre- 
sponding pair  of  transverse  wales,  so  that  they  did  not  inter- 
fere at  the  corners.  The  mold  was  twenty-nine  feet  in 
height. 

In  describing  this  mold,  Mr.  Powell  says:  "One  complete 
form  weighs  twenty-eight  tons;  each  piece  about  seven  tons. 
Each  piece  is  moved  separately  by  the  cable-way  in  forty-five 
to  sixty  minutes.  The  operation  of  removing  one  complete 
form  requires  from  three  to  four  hours  time.  After  being 
moved,  a  small  crew  of  men  occupy  nearly  a  day  in  plumbing 
and  bolting  together  the  form."  "The  boxes  containing  1.7 
cubic  yards  of  concrete  are  landed  on  top  of  the  form  by  cable- 
way  and  tipped  from  that  position.  Although  the  jar  and 
strain  is  severe,  the  forms  have  shown  no  ill  effects  therefrom, 
remaining  tight  and  secure." 


1  Major  Frederic  V.  Abbot  in  charge.     Mr.  A.  O.  Powell,  Asst    Engr., 
Report  Chief  of  Engineers,  1900,  p.  2778. 


358  CEMENT  AND  CONCRETE 

ART.  63.     DEPOSITION  OF  CONCRETE  IN  AIR. 

515.  Transporting  to  Place   of    Deposition.  —  In.  depositing 
the  concrete  in  place,  care  must  be  taken  not  to  undo  the  work 
of  mixing.     If  the  concrete  is  allowed  to  fall  freely  a  distance 
of  several  feet  or  to  slide  down  an  inclined  plane,  the  stones 
will  be  likely  to  separate  from  the  mass,  and  the  result  will  be 
a  layer  of  broken  stone  followed  by  a  layer  of  mortar.     If  the 
concrete  is  deposited  in  a  pile,  the  stone  will  roll  down  the  out- 
side of  the  cone.     This  action  is  especially  bad  in  concrete  that 
is  mixed  rather  dry.     The  author  has  seen  a  pavement  founda- 
tion in  which  the  limits  of  each  wheelbarrow  load  of  concrete 
could  be  distinguished,  the  foundation  presenting  the  appear- 
ance of  the  cross-section  of  a  honeycomb,  made  up  of  irregular 
hexagons    outlined    by    broken   stone    having    a    deficiency    of 
mortar.     In  all  such  cases,  if  the  action  cannot  be  avoided  by 
some  other  method  of  dumping,  then  care  must  be  taken  to 
remix  the  concrete. 

There  is  one  method  by  which  the  concrete  may  be  deposited 
by  gravity  without  separation  of  the  materials.  This  consists 
in  allowing  the  material  to  slide  down  a  tube,  but  the  tube 
must  be  kept  continually  full,  the  concrete  being  allowed  to 
run  out  at  the  bottom  only  as  fast  as  it  is  filled  in  at  the  top. 
This  method  is  only  applicable  where  the  mixing  is  continuous, 
as  in  the  case  of  machine  mixers. 

516.  Sometimes  it  will  be   found  possible  to  mix  the  con- 
crete so  near  to  the  place  of  deposition  that  it  may  be  shoveled 
directly  into  place.     In  mixing  by  hand  this  is  practicable,  as 
the  mixing  platforms  may  usually  be  easily  moved,  and  this 
method  of  deposition  is  carried  out  even  in  street  work  where 
the  concrete  is  in  thin  layers  and  hence  requires  much  moving 
of  platforms. 

Where  a  machine  mixer  is  used  that  is  so  mounted  as  to  be 
portable,  the  concrete  may  be  delivered  in  place  by  a  belt 
conveyor.  Such  an  arrangement  for  the  building  of  walls  and 
for  foundations  of  pavements,  has  already  been  described  in 
Chapter  XIV. 

The  conditions  are  usually  such,  however,  as  to  preclude  the 
possibility  of  mixing  the  concrete  so  close  to  the  work  that  it 
may  be  shoveled  into  place  or  handled  economically  on  a  con- 


PLACING  IN  AIR  359 

veyor  of  the  style  mentioned.  The  next  cheapest  method  is 
to  use  a  derrick  to  handle  skips  or  bottom-dump  buckets,  pro- 
vided the  work  is  sufficiently  concentrated  to  have  one  posi- 
tion of  the  derrick  serve  to  place  a  large  quantity  of  con- 
crete. The  skips  should  hold  about  a  cubic  yard,  and  if  a  batch 
mixer  is  used,  the  skip  should  hold  a  batch,  whatever  that 
may  be. 

517.  If  the  concrete  is  mixed  on  the  same  level  and  within 
less  than  two  hundred  feet  of  the  work,  wheelbarrows  may  be 
used,  but  for  greater  distances,  carts,  or,  what  is  usually  cheaper, 
cars  running  on  a  track,  should  be  employed. 

For  large  masses  of  concrete  a  cableway  may  be  employed 
to  advantage,  provided  there  is  sufficient  use  for  it  to  repay 
the  high  original  cost  of  plant.  The  selection  to  be  made  from 
among  these  common  methods  is  dependent  on  economy  as  in 
handling  other  material,  the  only  requirements  being  that  the 
concrete  shall  be  conveyed  to  place  quickly,  and  that  the  ma- 
terials shall  not  be  allowed  to  separate  as  a  result  of  any  of  the 
manipulation.  In  laying  large  quantities  of  concrete,  the  dif- 
ference between  success  and  failure  from  a  financial  standpoint 
may  easily  rest  in  the  proper  transportation  of  the  materials 
to  and  from  the  mixer. 

518.  Ramming.  —  The  concrete  should  be  deposited  in  hori- 
zontal layers  about  six  inches  thick,  leveled  with  a  shovel  and 
thoroughly  rammed.     The  length  of  time  ramming  should  be 
continued  and  the  vigor  with  which  it  should  be  done  depend 
largely  on  the  degree  of  plasticity  of  the  concrete.     If  the  con- 
crete is  made  of  such  a  consistency  that  when  struck  a  smart 
blow  with  the  back  of  a  shovel  a  film  of  moisture  will  just  show 
on  the  surface,  it  should  have  vigorous  ramming  to  insure  a 
compact  mass.     A  flushing  of  water  to  the  surface  will  then 
indicate  when  to  cease  tamping. 

With  a  little  more  water  there  is  less  danger  of  the  larger 
stones  " bridging"  and  leaving  large  voids  in  the  mass,  and 
less  work  will  be  required  to  flush  water  to  the  surface.  With 
such  a  consistency,  cutting  the  mass  with  a  spade  before  start- 
ing, the  ramming  may  assist  in  expelling  air  bubbles  and  pre- 
venting voids.  With  still  wetter  mixtures  ramming  becomes 
difficult,  as  the  concrete  will  soon  begin  to  quake,  after  which 
the  ramming  should  not  be  long  continued  as  the  mass  is  then 


360  CEMENT  AND  CONCRETE 

semi-fluid,  and  the  stones  may  gradually  work  themselves  to 
the  bottom  of  the  layer,  forcing  the  mortar  to  the  top. 

519.  Rammers  are  frequently  made  of   wood,  but  those  of 
iron  are  believed  to   be  better.     The   weight  of  a   rammer  is 
limited  by  the  capacity  for  work  of  the  man  who  wields  it. 
They  are  usually  made  to  weigh  from  twenty  to  forty  pounds. 
If  a  man  lifts  and  drops  a  forty-pound  rammer  with  forty  square- 
inch  face  twenty  times  a  minute,  he  is  doing  less  good  to  the 
concrete  than  if  he  dropped  a  twenty-pound  rammer  with  twenty 
square-inch  face  forty  times  a  minute.     If  the  face  of  the  ram- 
mer exceeds  thirty-six  square  inches,  the  result  is  apt  to  be  a 
mere  patting  of  the  surface  of  the  concrete,  unless  the  rammer 
is  so  heavy  as  to  require  two  men  to  operate  it.     Iron  rammers 
with  face,-  say,   three  by  six  inches,   and  weighing  twenty  to 
thirty  pounds,  are  believed  to  be  the  most  efficient.     Still  thinner 
rammers  than  this  may  be  necessary  in  work  involving  such 
detail  as  for  filling  in  between  iron  beams,  and  are  desirable 
for  tamping  near  the  face  of  the  mold. 

520.  Rubble  Concrete.  —  In  massive  work  the  embedding  of 
stones  of  "one-man  size,"  or  larger,  in  the  concrete  is  a  practice 
that  has  long  been  in  vogue.     The  objection  is  sometimes  made 
that  this  interferes  with  the  homogeneity  of  the  wall  and  that 
variations  in  expansion  may  result  in  injury  to  the  work.     It 
is  thought,  however,  that  in  large  masses  this  danger  is  more 
theoretical  than  real,  and  the  author  sees  no  objection  to  this 
form  of  construction  for  many  purposes  if  properly  carried  out, 
and  it  is  frequently  permitted  in  important  works.     Thin  walls, 
the  arch  rings  of  bridges,  shallow  foundations,  etc.,  should  not 
of  course  be  built  in  this  way,  because  the  stresses  to  which  such 
structures  are  subjected  should  be  met  by  a  uniform  resistance, 
to  avoid  the  effects  of  eccentric  or  irregular  loading.     In  such 
structures   as   dams,   lock   walls,   breakwaters,   retaining   walls, 
and  in  many  cases  bridge  piers  and  abutments,  the  work  may 
be  considerably  cheapened  without  sacrificing  the  fitness  of  the 
structure.     The    stones    thus    embedded    should    be    perfectly 
sound  and  should  not  lie  nearer  one  to  another  than  six  inches, 
nor  should  they  lie  nearer  than  this  to  the  face  of  the  wall. 
The  concrete  should  be  mixed  rather  wet,  and  much  care  taken 
that  each  stone  is  completely  surrounded  by  a  compact  mass  of 
concrete.     The  stones  should  be  settled  into  the  concrete  al- 


PLACING  IN  AIR  361 

ready  laid  far  enough  to  assure  their  having  a  full  bed.     Stones 
used  in  this  manner  are  sometimes  called  "  plums." 

521 .  Another    class   of    rubble   concrete    differing   from   the 
above  more  in  degree  than  in  kind,  is  formed  by  placing  large 
stones  in  the  work,  and  filling  the  joints  between  them  with  a 
rath?r  wet  concrete  in  which  spalls  may  be  rammed  if  desired. 
The  difficulty  of  obtaining  a  compact  wall  by  this  method  is 
perhaps  a  little  greater  than  when  smaller  stone  are  used,  but 
in  either  case  if  really  water-tight  work  is  desired,  the  inspec- 
tion must  be  thorough. 

The  saving  in  cost  by  the  use  of  rubble  concrete  depends 
upon  the  local  conditions,  but  under  ordinary  circumstances 
when  broken  stone  is  employed,  the  cost  of  crushing  the  stone 
and  the  cost  of  cement,  for  a  volume  of  concrete  equal  to  the 
volume  of  the  stone  imbedded,  are  practically  saved. 

522.  Joints    in    Concrete.  —  In    the    construction    of    large 
masses  of  concrete  in  place,  joints  cannot  be  avoided;  that  is, 
it  is  not  possible  to  make  the  entire  mass  monolithic,  as  force 
enough  could  not  be  employed  to  carry  up  the  entire  struc- 
ture at  once.     Even  if  this  were  possible,  it  would  not  be  de- 
sirable, since  the  changes  in  length  of  the  wall  due  to  changes 
in  temperature  would  probably  result  in  cracks  which  would 
be  irregular  in  outline  and   mar  the  appearance  of  the   wall, 
if  they  had  no  more  serious  effect. 

When  the  concrete  is  subjected  to  vertical  forces  only,  as 
in  foundations  for  buildings,  horizontal  joints  are  less  objec- 
tionable than  vertical  joints.  But  in  the  construction  of  con- 
crete lock  walls,  dams,  and  breakwaters,  vertical  joints  are  de- 
sirable to  confine  the  cracks  to  predetermined  planes.  In  the 
building  of  such  structures,  therefore,  the  method  has  been 
adopted  of  dividing  the  work  into  sections  of  such  horizontal 
dimensions  as  may  be  thought  best,  and  completing  each  sec- 
tion as  a  monolith.  This  will  sometimes  require  the  contin- 
uous prosecution  of  work  for  twenty-four  or  forty-eight  hours. 
Whether  this  method,  involving  work  at  night,  which  is  always 
more  expensive  and  usually  less  thorough,  is  justified  by  the 
end  sought,  depends  upon  the  character  of  the  structure. 

523.  If  this  method  is  not   adopted,  and  a  horizontal  plane 
of  weakness  is  a  serious  defect,  special  means  should  be  pro- 
vided for  avoiding  this  plane  of  weakness.     Such  provision  may 


362  CEMENT  AND  CONCRETE 

be  made  by  iron  dowels  set  in  the  concrete  at  the  end  of  the 
days  work  and  projecting  above  the  surface  to  be  covered  by 
the  concrete  placed  the  next  day;  steps  or  hollows,  or  grooves 
parallel  to  the  length  of  the  wall,  may  be  left  to  be  filled  by 
the  next  layer.  Large  stones  weighing  a  hundred  pounds  or 
more  are  frequently  imbedded  one  half  their  depth  in  the 
last  layer  of  a  days  work  to  form  a  bond  with  the  following 
layer. 

In  any  case  special  care  should  be  taken  to  thoroughly  wash 
and  clean  the  surface  of  hardened  concrete  before  continuing 
the  work,  using  preferably  wire  brooms  for  this  purpose  and 
removing  any  stones  at  the  surface  that  appear  to  be  loose. 
A  thin  layer  of  rich  cement  mortar  should  then  be  laid  upon  it, 
into  which  the  first  layer  of  fresh  concrete  is  well  rammed. 

If  the  appearance  of  the  finished  face  is  of  importance,  special 
care  must  also  be  exercised  in  joining  at  this  point.  Before 
leaving  a  layer  which  is  to  be  allowed  to  harden  before  contin- 
uing the  work,  the  line  limiting  the  height  of  the  concrete  at 
the  face  should  be  made  perfectly  horizontal,  for  a  slight  crack, 
or  at  least  a  noticeable  line,  may  be  expected  at  this  point,  and 
if  not  straight  it  will  be  the  more  unsightly. 

524.  If  for  any  reason  a  layer  of  concrete  cannot  be  carried 
over  the  whole  area  of  the  wall  or  foundation,  it  should  never 
be  allowed  to  taper  off  to  a  wedge,  but  a  plank  equal  in  width 
to  the  thickness  of   the  layer  should  be  set  on  edge,  firmly   se- 
cured, and  the  concrete  tamped  against  it.     In  the  construction 
of  arches,  culverts  and  sewers,  such  stop  planks  may  well  be  set 
normal  to  the  surface  of  the  intrados  instead  of  vertical.     In 
case  more  than  one  layer  is  left  incomplete,   they  should  be 
stepped  back,  making  an  offset  for  each  layer  of  at  least  one  or 
two  feet.     The  concrete  should  never  be  built  up  on  a  smooth 
batter  if  new  concrete  is  to  be  joined  to  it  later. 

525.  Keeping  Concrete  Moist.  —  All  concrete  should  be  kept 
moist  from  the  time  it  is  in  the  wall  until  it  has  become  well 
hardened.     Surfaces    exposed   to    the    air   should   therefore   be 
sprinkled   frequently   for   at   least   several   days   after   placing. 
An  excellent  practice  is  to  cover  the  surface  with  burlaps  which 
may  be  kept  saturated,  as  this  not  only  furnishes  the  necessary 
moisture,  but  protects  the  work  from  the  direct  rays  of  the 
sun.     The  interior  of  a  large  mass  will  probably  take  care  of 


SURFACE  FINISH  363 

itself  in  this  regard,  but  the  precaution  has  sometimes  been 
taken  of  leaving  vertical  holes  or  wells  in  the  mass,  which  are 
kept  filled  with  water  for  some  weeks  and  are  then  filled  with 
concrete. 

523.  FINISH.  —  Some  of  the  precautions  that  must  be  taken 
to  secure  a  good  finish  to  the  face  of  concrete  work  have  al- 
ready been  mentioned  in  considering  the  forms  and  the  meth- 
ods of  deposition.  These  are  usually  supplemented,  however, 
by  certain  special  means  when  the  appearance  is  of  much  im- 
portance. 

We  must  say  first,  that  the  application  of  a  plaster  of  ce- 
ment mortar  to  a  finished  and  set  concrete  face  will  almost 
never  be  permanent.  It  is  seldom  that  it  will  adhere  with  suf- 
ficient strength  to  prevent  scaling  due  to  differences  in  expan- 
sion of  the  materials  of  different  composition  and  age.  If 
plaster  must  be  used  on  the  face  of  a  wall,  it  should  be  applied 
before  the  concrete  has  set,  but  it  is  safer  to  avoid  plastering. 
It  is  of  course  advisable  to  fill  with  rich  mortar  any  voids  that 
may  appear  in  the  face  of  the  work,  but  such  places  should  be 
few. 

If  the  molds  are  removed  while  the  concrete  is  still  moist, 
the  face  may  be  coated  with  a  thin  grout  and  then  immediately 
scraped  off  with  the  edge  of  a  trowel.  This  results  in  filling  the 
small  voids  in  the  face  of  the  work,  but  does  not  leave  a  coat  of 
plaster  on  the  surface  to  scale  off. 

527.  A  good  finish  may  be  obtained   when  the   molds  are 
smooth  if  the  workmen  will  force  the  blade  of  a  spade  or  shovel 
between  the  fresh  concrete  and  the  mold,  and  pull  the  handle 
away  from  the  mold.     This  has  the  effect  of  forcing  the  large 
stone  back  from  the  face  and  allowing  the  mortar  to  flow  in.     A 
layer  of  mortar  is  thus  left  next  the  mold  with  no  marked  line 
of  junction  between  mortar  and  concrete,  as  may  be  the  case*  in 
using  a  mortar  facing.     A  similar  effect  may  be  produced  by 
throwing  the  concrete  against  the  face  of  the  mold  with  such 
force  that  the   larger  pieces   of   aggregate   rebound.       In  very 
finely  finished  work  this  may  mar  the  surface  of  the  sheathing, 
but  ordinarily  this  method  is  effective. 

528.  When  a  special  layer  of  mortar  is  used  for  facing,  there 
is  more  danger,  perhaps,  of  making  the  layer  too  thick  than  too 
thin.     As  to  the  richness  of  the   mortar,   two  parts  sand  by 


364  CEMENT  AND  CONCRETE 

measure  to  one  volume  packed  cement  is  usually  sufficient, 
though  a  more  glossy  finish  may  be  made  if  desired,  by  using 
equal  parts  of  cement  and  sand.  It  is  better  to  avoid  too  great 
a  variation  between  the  richness  of  the  mortar  used  for  facing 
and  that  used  in  the  body  of  the  concrete. 

One  of  the  best  ways  of  applying  such  a  layer  is  to  prepare  a 
sheet  of  steel  of  width  equal  to  the  thickness  of  one  layer  of  con- 
crete, usually  six  to  eight  inches,  with  two  handles  on  the  upper 
edge  to  facilitate  moving  it.  At  the  ends  of  the  sheet,  on  the 
side  next  the  mold,  rivet  short  pieces  of  1J  in.  by  1J  in.  or  2  in. 
by  2  in.  angle  iron.  This  sheet  of  iron  with  the  projecting  legs 
of  the  angles  against  the  face  of  the  molds,  forms,  with  the 
latter,  a  space  one  and  one-half  or  two  inches  thick,  which 
is  to  be  entirely  filled  with  the  finishing  mortar  made  rather 
moist  and  tamped  lightly  with  edge  rammers.  The  concrete  is 
filled  in  behind  the  iron,  after  which  the  latter  is  withdrawn  by 
means  of  the  handles,  and  the  whole  mass  is  thoroughly  rammed. 
The  end  sought  is  that  the  finishing  mortar  shall  have  some 
approximately  definite  thickness,  and  that  the  stones  of  the 
concrete  shall  be  tamped  into  the  finishing  mortar,  but  not 
through  it,  and  thus  destroy  any  sharp  line  of  demarcation 
between  mortar  and  concrete,  and  ensure  a  perfect  bonding  of 
the  two.  It  is  evident  that  this  can  only  be  accomplished  by 
placing  the  mortar  and  concrete  at  the  same  time. 

529.  One  other  cautionary  remark  concerning  the  use  of  fin- 
ishing mortar.  With  the  present  state  of  our  knowledge  con- 
cerning the  rates  of  expansion  of  mortars  and  concretes  of  dif- 
ferent composition,  it  is  not  considered  wise  to  use  too  many 
combinations  in  the  same  structure.  To  illustrate,  a  pavement 
or  surfacing  of  a  large  concrete  structure  was  once  built  in  layers 
as  follows:  first,  thick  natural  cement  grout  was  placed  on  the 
concrete  foundation;  second,  natural  cement  concrete;  third, 
Portland  cement  concrete;  fourth,  a  richer  Portland  cement 
concrete;  fifth,  Portland  granolithic;  sixth,  rich  Portland  mortar; 
and  seventh,  floated  with  dry  Portland  cement  and  sand.  We 
cannot  be  absolutely  sure  that  this  is  bad  practice,  but  it  would 
seem  that  this  structure  might  have  served  its  purpose  with 
fewer  varieties  of  material,  and  it  is  usually  considered  very 
doubtful  whether  Portland  cement  mixtures  will  always  ad- 
here well  to  mixtures  of  natural  cement,  although  the  author 


SURFACE    FINISH  365 

knows  of  instances  where  they  have  been  used  in  juxtaposition 
apparently  with  good  results. 

530.  Granolithic  is   a  facing  or  surfacing  mortar  composed 
of  crushed  granite  and  cement.     The  granite  is  usually  specified 
to  contain  no  particles  larger  than  f  inch  to  one  inch,  and  about 
one  and  one-half  to  two  and  one-half  parts  are  used  to  one  vol- 
ume of  cement.     This  is  more  frequently  used  for  foot  walks 
and  other  places  where  resistance  to  wear  is  required,  but  may 
also  be  used  to  surface  walls,  to  line  reservoirs,  etc.     It  will  be 
mentioned  again  in  connection  with  cement  sidewalk  construc- 
tion. 

531.  Exposed  concrete  surfaces    frequently  present  a  patchy 
appearance.     This  may  be  the  result  of  lack  of  care  in  placing 
the  concrete  next  the  mold,  or  it  may  be  due  to  variations  in 
the  purity  of  the  sand  or  in  the  amount  of  water  used  in  mixing. 
On  mortar-faced  work  this  lack  of  uniformity  is  less  noticeable. 
The  use  of  slag  sand,  or  of  a  little  fine  pozzolanic  material,  may 
be  advantageous,  and  a  small  amount  of  lampblack  in  the  facing 
mortar  also  tends  towards  uniformity  in  appearance. 

A  very  pleasing  finish  may  be  given  by  applying  to  the  set 
concrete  a  thin  wash  of  cement  and  plaster  of  Paris,  though  the 
permanence  of  such  a  wash  may  be  open  to  question.  The 
sheathing  should  be  removed  as  early  as  it  is  perfectly  safe  to 
do  so,  and  the  concrete  surface  cleaned  from  any  oil  or  grease 
that  may  have  come  from  the  mold  planks.  The  wash,  which 
should  be  very  thin,  may  be  applied  with  a  whitewash  brush. 
A  mixture  of  equal  parts  Portland  cement  and  plaster  of  Paris 
gives  a  very  light  gray  finish,  and  one  part  plaster  to  three  parts 
cement  gives  a  trifle  darker  shade. 

532.  A  rubbed  finish  of  excellent  appearance  may  be  given 
by  removing    the  sheathing   before  the  concrete  has  set   very 
hard,  say  after  twenty-four  to   forty-eight   hours,  and   rubbing 
the  surface  with  white  brick  or  with  a  wooden  float.     If  there 
are  small  voids  in  the  surface,  it  may  be  covered  with  a  thin 
grout    of    equal    parts   of    cement  and  sand    and  then  rubbed 
hard  with  a  circular  motion.     The  grout  should  not  leave  a 
scale  on  the  work,  the  object  being  only  to  fill  surface  imperfec- 
tions. 

If  the  mold  boards  are  removed  at  just  the  proper  time,  a 
good  finish  may  be  given  by  rubbing  with  a  wooden  float,  with- 


366  CEMENT  AND  CONCRETE 

out  the  coating  of  thin  grout.  A  somewhat  similar  effect  is 
produced  by  brushing  the  surface  with  brooms  or  stiff  brushes. 

533.  "  Pebble-dash."  —  What  is  called  a  pebble-dash  finish 
was  used  in  the  construction  of  a  bridge  in  the  National  Park  at 
Washington,  D.  C.1  Eighteen  inches  of  the  concrete  next  the 
face  was  made  of  one  part  cement,  two  parts  sand,  and  five  parts 
of  gravel  and  rounded  stone  from  one  and  one-half  to  two  inches 
in  their  smallest  diameter.  After  the  removal  of  the  forms  the 
cement  and  sand  were  b  rushed  from  around  the  face  of  the  gravel 
next  the  surface  exposed  to  view.  It  was  found  by  experiment 
that  the  brushing  should  be  done  when  the  concrete  was  about 
twenty-four  hours  old.  At  twelve  hours  the  gravel  was  displaced 
by  the  brushing,  and  after  thirty-six  hours  the  mortar  had  be- 
come so  hard  as  to  be  removed  from  the  surface  of  the  stones 
with  difficulty.  The  forms  were  therefore  designed  so  that 
sections  'of  the  lagging  could  be  removed  as  desired.  The  cost 
of  the  brushing  was  said  to  be  about  sixty  cents  per  square  yard. 

A  somewhat  similar  method  is  employed  in  giving  to  con- 
crete the  appearance  of  cut  stone.  The  materials  used  in  the 
surfacing  mortar  are  Portland  cement  and  crushed  rock,  the 
character  of  the  rock  depending  upon  the  color  and  texture  de- 
sired in  the  finish.  The  molds  having  been  removed  after  the 
proper  time  has  elapsed,  the  mortar  covering  the  face  of  the 
particles  of  crushed  rock  is  removed  by  brushing  or  by  washing 
the  surface  with  a  weak  acid  solution,  followed  by  clean  water, 
and  finally  by  an  alkaline  solution  to  prevent  any  further  action 
of  traces  of  the  acid  which  might  be  left  on  the  face.  This  last 
method  is  said  to  be  patented,  "the  patent  covering  the  obtain- 
ing of  a  natural  stone  finish  for  concrete  by  mechanical,  chemi- 
cal or  other  means."  2  It  is  hoped  that  such  a  blanket  patent  is 
somewhat  less  formidable  than  it  appears. 

If  the  sheathing  planks  of  the  molds  can  be  removed  about 
twenty-four  hours  after  the  concrete  is  placed,  the  same  effect 
may  be  produced  without  the  use  of  acid.  By  using  plenty  of 
water  the  cement  and  finer  portions  of  crusher  dust  in  the  face 


1  Capt.   Lansing  H.  Beach,  Corps  of  Engrs.,  U.  S.  A.,  in  charge.     Work 
described  by  Mr.  W.  I.  Douglas,  Engr.  of  Bridges,  D.  C.,  Engineering  News, 
Jan.  22,  1903. 

2  Engineering  News,  May  21,  1903, 


SURFACE   FINISH  367 

may  be  washed  out  with  a  stiff  corn  broom,  leaving  the  facets 
of  the  crushed  rock  exposed. 

534.  Pointing    and    Bush-hammering.  —  If   the  molds  have 
been  left  in  place  until  the  concrete  is  set  hard  and  it  is  found 
that  the  face  of  the  concrete  is  not  what  is  desired,  it  may  still 
be  improved  although  it  may  not  be  plastered.     With  this  ob- 
ject the  face  is  sometimes  tooled  with  the  stone  cutter's  point  to 
give  the  appearance  of  rough  pointed  or  rock  face  masonry. 
Grooves  may  be  cut  to  block  off  the  work  into  rectangles  of  the 
proper  size,  then  a  draft  of  one  to  two  inches  may  be  left  along 
all  of  these  artificial  joints,  and  within  the  draft  line  the  rough 
pointing  may  be  done. 

A  cheaper  method,  however,  is  to  bush-hammer  the  entire 
face,  and  this  tends  to  mask  any  lack  of  uniformity  in  color  or 
smoothness.  Hush-hammering  may  be  done  by  ordinary  labor- 
ers at  a  small  cost,  as  one  man  can  go  over  from  fifty  to  one 
hundred  square  feet  in  ten  hours,  making  the  cost  from  1-J  cents 
to  3^  cents  per  square  foot,  with  labor  $1.75  per  day.  Where  it 
is  decided  beforehand  to  bush-hammer  the  work,  less  pains  need 
be  taken  in  dressing  the  lagging  of  the  forms. 

535.  Colors  for  Concrete  Finish.  — The  addition  of  coloring 
matter  to  cement  and  concrete  is  not  at  present  widely  prac- 
ticed, and  consequently  experience  has  not  been  sufficient  to  in- 
dicate just  what  colors  may  be  used  without  detriment  to  the 
work.     Lampblack  has  been  most  commonly  employed,  giving 
different  shades  of  gray  according  to  the  amount  used.     In  any 
large  work  where  the  use  of  coloring  matter  is   desirable  and 
there  is  not  time  to  institute  thorough  tests,  the  advice  of  a 
cement   chemist   should   be   sought.     The   dry   mineral    colors, 
mixed  in  proportions  of  two  to  ten  per  cent,  of  the   cement, 
give  shades  approaching  the  color  used.     Bright  colors  are  diffi- 
cult to  obtain  and  would  not  be  in  keeping  with  a  masonry 
structure  except  in  architecture. 

When  mixed  with  an  American  Portland  cement  mortar, 
containing  one  part  cement  to  two  parts  by  weight  of  a  yellow 
river  sand,  the  particles  of  which  are  largely  quartz,  the  colors 
indicated  in  the  following  table  are  obtained. 

With  no  coloring  matter  added,  the  mortar  was  a  light  green- 
ish slate  when  dry.  Ultra  marine  green,  in  amounts  up  to  8 
per  cent,  of  the  cement,  had  no  apparent  effect  on  the  color  of 


368 


CEMENT  AND  CONCRETE 


this  mortar.  Variations  in  character  of  cement  and  sand  will 
affect  the  result  obtained  in  using  coloring  matter.  The  colors 
indicated  below  are  for  dry  mortars  ;  when  the  mortar  is  wet 
the  shades  are  usually  darker.  None  of  the  materials  mentioned 
in  the  table  seems  to  affect  the  early  hardening  of  the  mortar, 
though  very  much  larger  proportions  might  prove  injurious. 
With  red  lead,  however,  even  one  per  cent,  is  detrimental,  and 
larger  proportions  are  quite  inadmissible. 

COLORED   MORTARS. 

Colors   Given   to   Portland  Cement  Mortars  Containing  Two  Parts 
River  Sand  to  One  Cement. 


.|o 

DRY 

WEIGHT  OF  DRY  COLORING  MATTER  TO  100  POUNDS  OF  CEMENT. 

Ir  j 

MATERIAL 

^  E 

USED. 

""S  *-" 

i  Pound. 

1  Pound. 

2  Pounds. 

4  Pounds. 

II 

Dark   Blue 

Lamp  Black 

Light  Slate     . 

Light  Gray 

Blue  Gray  . 

Slate      . 

15 

Prussian 

Light  Green 

Light  Blue 

Bright  Blue 

Blue     .     . 

Slate      .     . 

Slate  .     .     . 

Blue  Slate  . 

Slate      . 

50 

Ultra  Marine 

Light  Blue 

Bright  Blue 

Blue 

Slate  .     .     . 

Blue   Slate 

Slate  . 

20 

Yellow 

Ochre  .     . 

Light  Green  . 

. 

Light  Buff 

3 

Burnt 

Light  Pinkish 

Dull  Laven- 

Umber 

Slate      .     . 

Pinkish  Slate  . 

der  Pink 

Chocolate  . 

10 

Venetian 

Slate,  Pink 

Bright  Pinkish 

Light  Dull 

Red     .     . 

Tinge     .     . 

Slate  .     .     . 

Pink  .     . 

Dull  Pink 

2£ 

Chattanooga 

Light  Pinkish 

Light  Terra 

Light  Brick 

Iron  Ore  . 

Slate      .     . 

Dull  Pink  .     . 

Cotta  .     . 

Red  .     . 

2 

Light  Brick 

Red  Iron  Ore 

Pinkish  Slate 

Dull  Pink  .     . 

Terra  Cotta 

Red    .     . 

2* 

536.  In  some  cases  it  may  be  sufficient  to  color  the  surface 
of  the  work  by  painting.  Ordinary  oil  paints  are  sometimes 
applied  after  washing  the  surface  of  the  wall  with  very  dilute 
sulphuric  acid,  one  part  acid  to  100  parts  water,  but  the  per- 
manence of  such  a  finish  seems  very  questionable. 

The  method  of  obtaining  a  gray  finish  by  painting  with  a 
thin  grout  of  cement  and  plaster  of  Paris  has  already  been  de- 
scribed (§  531).  Similar  methods  may  be  used  with  the  dry 
mineral  colors,  and,  while  their  permanency  cannot  be  vouched 
for,  it  seems  a  more  reasonable  procedure  than  to  paint  a  con- 


PLACING   UNDER   WATER  369 

crete  surface  with  oil  paints.  One  pound  red  iron  ore  to  ton 
pounds  cement  mixed  dry,  and  then  made  into  a  very  thin  grout 
and  applied  to  a  well  cleaned  concrete  surface  with  a  white- 
wash brush,  gives  a  pleasing  brick-red  color;  and  a  rich  dark 
red  is  given  by  one  pound  red  iron  ore  to  three  pounds  cement. 
The  earlier  this  is  applied  after  the  concrete  has  set,  the  more 
likely  is  it  to  remain  permanent. 

ART.  64.     PLACING  CONCRETE  UNDER  WATER 

537.  In  building  a  concrete  structure  under  water  where  the 
site  cannot  be  coffered,  it  must  be  expected  that  the  expense 
of  the  work  will  be  increased,  and  the  quality  of  concrete  poorer. 
The   methods  employed  for  subaqueous   construction  are:  1st, 
the  laying  of  freshly  mixed  concrete  in  roughly  prepared  forms; 
2d,  placing  the  fresh  concrete  in  bags  of  burlap  or  canvas  which 
are  deposited  while  the  concrete  is  still  soft;  and  3d,  molding 
in  air  concrete  blocks  which  are  placed  in  the  work  when  well 
set. 

In  the  first  method  some  cement  will  certainly  be  washed 
out  of  the  concrete,  the  extent  of  this  loss  depending  upon  the 
condition  of  the  water  in  which  the  work  is  done  (i.e.,  its  depth 
and  the  amount  of  current  and  wave  action)  and  the  care  with 
which  the  concrete  is  lowered  to  place.  Tamping  cannot  be 
done  with  this  method,  and  any  movement  of  the  concrete  to 
level  it  will  cause  further  loss  of  cement. 

In  the  second  method  the  loss  of  cement  will  be  much  less, 
but  the  adhesion  between  the  different  masses  will  be  slight.  In 
the  third  method  there  is  no  loss  of  cement  and  the  concrete 
can  be  well  rammed ;  but  if  small  blocks  are  used,  there  may 
be  difficulty  in  so  placing  them  under  water  as  to  make  a  solid 
structure,  while  if  large  blocks  are  used,  special  hoisting  ma- 
chinery is  required  to  handle  them. 

538.  DEPOSITING    IN    PLACE.—  The  first  method  mentioned 
above,  depositing  fresh  concrete  in  place,  is  usually  the  cheap- 
est and   most  expeditious   method,   though  it  is  not  likely  to 
dve  the  best  results.     When  concrete  is  lowered  through  water, 
there  is  a  tendency  for  the  cement  to  separate  from  the  sand 
and   stone.     This   tendency  seems  to  be  exhibited  in  a  more 
marked  degree  with  some  cements  than  with  others.     In  con- 
nection with  the  construction  of  the  concrete  foundations  of 


370  CEMENT  AND  CONCRETE 

the  Charlestown  bridge,  a  test  was  devised  for  determining  the 
relative  values  of  the  different  lots  of  cement  for  depositing  in 
water.1  Concrete  was  laid,  through  a  small  chute,  in  a  cement 
barrel  placed  in  a  hogshead  filled  with  salt  water.  It  was  found 
that  while  some  specimens  would  retain  their  form  after  twenty- 
four  hours  when  the  barrel  was  removed,  others  showed  but 
little  cohesion  after  twenty-four  to  forty-eight  hours.  In  the 
former,  the  cement  and  gravel  remained  well  distributed  through- 
out the  mass,  but  in  the  latter  much  of  the  cement  had  sepa- 
rated from  the  gravel,  and  settled  in  the  bottom  of  the  barrel, 
where  it  remained  in  an  inert  state,  while  the  central  portion  of 
the  concrete,  robbed  of  its  cement,  had  many  voids.  As  a 
result  of  this  test,  some  lots  of  cement  were  not  accepted  for 
use. 

The  finest  portion  of  the  cement  is  very  liable  to  separate 
from  the  remainder  as  the  concrete  passes  through  the  water, 
and  if  subjected  to  the  action  of  waves  or  a  current,  much  of 
the  cement  will  be  washed  away.  In  exposed  situations  it  is 
especially  necessary  to  inclose  the  site  of  the  work  with  sheet  pil- 
ing or  cribs,  or  a  wall  constructed  by  the  bag  or  block  method. 
When  the  water  level  outside  the  form  is  constantly  changing, 
the  flow  of  water  through^  the  joints  in  the  sheathing  is  especi- 
ally effective  in  washing  out  the  cement,  and  in  such  conditions 
the  sheathing  should  be  made  as  nearly  water-tight  as  possible. 
To  this  end  tongue  and  groove  lagging  may  t>e  used,  or  the  face 
of  the  mold  may  be  covered  with  tarred  felt,  or  canvas,  tacked 
in  place. 

539.  Laitance  is  the  term  applied  to  the  whitish  spongy 
material  that  is  washed  out  of  concrete  when  it  is  deposited  in 
water.  Before  settling  on  the  surface  of  the  concrete,  which 
it  does  slowly,  it  gives  to  the  water  a  milky  appearance,  hence 
the  name.  In  fresh  water  this  semi-fluid  mass  is  composed  of 
the  finest  flocculent  matter  in  the  cement,  containing  generally 
hydrate  of  lime.  It  remains  in  a  semi-fluid  condition  for  a 
long  time  and  acquires  very  little  hardness  at  the  best.  In  sea 
water  the  laitance  is  more  abundant  and  is  made  up  of  silica, 
lime  and  magnesia,  with  carbonic  acid  and  alumina,  its  exact 


1  Report  of  Mr.  William  Jackson,  Chief  Engineer.     Third  Annual  Report 
Boston  Transit  Commission. 


PLACING   UNDER  WATER  371 

composition  depending  upon  the  character  of  the  cement.  This 
interferes  seriously  with  the  bonding  of  the  layers  of  concrete, 
and  when  it  has  settled  it  should  be  cleaned  from  the  surface 
before  another  layer  is  placed. 

540.  The  Tremie.  —  A  method  frequently  employed  to  pre- 
vent, as  much  as  possible,  the  loss  of  cement,  is  to  make  use  of 
a  large  tube  of  wood  or  sheet  iron,  made  in  sections  so  that 
its  length  is  adjustable,  and  provided  with  a  hopper  at  the 
upper  end.  Such  a  tube  is  called  a  tremie.  The  hopper  is 
always  above  water,  and  the  lower  end  of  the  tube,  which  may 
also  terminate  in  a  hopper,  rests  upon  the  bottom  of  the  founda- 
tion. 

The  tremie  is  first  filled  with  concrete,  a  box  placed  over  the 
lower  end  serving  to  prevent  the  escape  of  the  concrete  while 
the  tube  is  being  lowered  until  the  end  rests  upon  the  bottom. 
The  tube  is  then  lifted  from  the  bottom  sufficiently  to  allow 
the  concrete  to  escape  as  fast  as  fresh  concrete  is  added  at  the 
top.  The  surface  of  the  concrete  in  the  tube  should  be  kept 
continuously  above  the  water  surface.  The  tremie  may  be 
held  in  position  by  a  crane,  or  it  may  be  so  supported  as  to  al- 
low of  two  motions  at  right  angles  to  each  other.  Such  an 
arrangement  was  used  in  building  the  piers  for  the  Boucicault 
Bridge,  the  tube  traveling  along  a  platform,  which  in  turn 
could  move  on  a  track  at  right  angles  to  the  first  motion.  In 
using  a  tremie  the  thickness  of  a  layer  may  be  regulated  at  will. 

In  the  construction  of  the  Charlestown  Bridge  1  a  tube  was 
used  fourteen  inches  in  diameter  at  the  bottom,  and  about 
eleven  inches  in  diameter  at  the  neck,  above  which  was  a  hopper 
to  receive  the  concrete.  When  the  attempt  was  made  to  place 
too  thick  a  layer  at  one  operation,  it  was  found  that  the  charge 
was  likely  to  be  lost,  and  the  best  results  were  believed  to  be 
obtained  with  layers  two  feet  to  two  and  one-half  feet  thick. 
Some  experiments  were  made  with  a  plug  designed  to  keep  the 
water  from  flowing  up  through  the  concrete  when  the  tube 
was  being  refilled  after  a  loss  of  the  charge.  This  plug  was 
made  with  a  central  core  of  wood  and  sides  of  canvas  expanded 
by  steel  ribs.  It  worked  fairly  well,  but  its  use  was  not  con- 
tinued. 


1  Third  Annual  Report,  Boston  Transit  Commission. 


372  CEMENT  AND  CONCRETE 

541.  This    principle  was  employed  by  Mr.  Daniel  W.  Mead 
in  placing  concrete  in  a  small  shaft  in   ninety  feet  of  water.1 
An  eight  inch,  wrought  iron  pipe  was  screwed  together  in  sec- 
tions, and  provided  with  a  hopper  at  the  upper  end  and  a  wooden 
plug  at  the  lower  end.     After  lowering  the  pipe  into  the  shaft, 
the  pipe  was  filled  with  concrete  and  it  was  expected  that  its 
weight  would  force  out  the  plug  at  the  bottom  when  the  pipe 
was  raised.     On  the  first  attempt,  however,  the  plug  failed  to 
drop  out,  and  on  raising  the  pipe  the  cause  was  apparent.     The 
plug  had  evidently  leaked,  and  as  the  first  concrete  was  dropped 
into  the  pipe  it  had  separated,  the  broken  stone  being  at  the 
bottom,  the  sand  next,  and  the  cement  above  had  so  plugged 
the  pipe  as  to  support  the  weight  of  the  concrete.     The  second 
attempt,   when  a  tighter  wooden  plug  was  used  and  a  small 
pipe  placed  inside  the  larger  one  to  assist  in  loosening  the  plug 
if  necessary,  was  successful. 

542.  The   Skip.  —  Since    in    submerged    work    the    concrete 
should  be  deposited  in  as  large  masses  as  possible,  the  use  of  a 
large  skip  will  probably  give  better  results  than  the  tremie. 
A  box  form  may  be  used  with  hinged  lids  at  the  top  to  permit 
filling,   and   two   hinged   doors   at   the  bottom   which   may   be 
opened  from  the  surface  by  a  tripping  rope  when  the  box  has 
reached  the  place  for  depositing  the  concrete. 

A  convenient  form  of  skip  is  made  in  two  halves,  each  half 
having  a  cross-section  either  of  a  right  angled  triangle  or  a 
quadrant  of  a  circle.  The  two  boxes  are  hinged  at  their  upper 
inside  corners  and  the  pieces  through  which  the  hinge  rod 
passes  are  prolonged  upward,  the  lowering  cables  being  at- 
tached to  their  ends.  Two  opening  cables  are  fastened  to  the 
outer  corners  of  the  boxes.  Two  sheets  of  iron  may  be  used 
as  covers  to  the  boxes,  being  attached  to  the  hinge  rod  that 
serves  for  the  two  halves  of  the  skip. 

It  is  seen  that  the  skip  will  work  on  the  principle  of  a  pair 
of  ice  tongs.  While  being  filled  with  concrete  the  box  is  sup- 
ported by  the  lowering  cables,  and  the  hinged  lids  are  kept  up 
by  some  simple  contrivance.  When  full,  the  lids  are  closed 
and  the  skip  lowered  till  it  rests  on  the  bottom;  the  skip  being 
then  hoisted  slowly  by  means  of  the  opening  cables,  the  con- 

1  Trans.  Assn.  of  Civil  Engineers  of  Cornell  University,  1898. 


PLACING   UNDER  WATER  373 

crete  is  gently  deposited  in  place.      Su?h  skips  are  supplied  by 
the  makers  of  concrete  machinery. 

543.  In  depositing  concrete  by  means  of  skips  it  is  well  to 
have  the  latter  of  large  size,  holding  not  less  than  a  cubic  yard, 
and  preferably  two  cubic  yards  or  more.     The  larger  quantity 
will   compact  itself  better  on   account  of  the  greater   weight, 
and  the  surface  which  is  subjected  to  wash  will  have  a  lesser 
area  in  proportion  to  the  volume  of  the  mass.     The  skip  should 
be  completely  filled  with  concrete  and  tightly  closed  while  it  is 
being  lowered.     It  is  important  also  that  the  skips  be  lowered 
slowly,  in  order  that  the  inclosed  air  may  be  replaced  by  water 
without  commotion. 

544.  The    Bag.  —  Mr.   Wm.   Shield  '   devised   a  bag  for  de- 
positing concrete  under  water  which  is  said  to  work  very  satis- 
factorily.    The  top  of  the  bag  is  closed,  and  has  a  three-quarter 
inch  wrought  iron  bar  fastened  across  the  end  with  a  loop  to 
receive  the  hook  of  the  lowering  line.     The  mouth  of  the  bag 
is  slightly  larger  than  the  upper  end,  to  facilitate  the  discharge 
of  the  concrete.     The  bag  is  inverted  to  be  filled,  and  the  mouth 
is  then  secured  by  a  turn  of  a  line  provided  with  loops  through 
which  a  small  tapering  pin  is  passed.     This  pin  is  attached  to 
a  tripping  line,  and  when  the  bag  has  reached  the  place  of 
deposition,  a  pull  of  the  tripping  line  releases  the  pin;  when 
the  bag  is.  gently  lifted,  the  concrete  is  deposited  in  place  with 
such  slight  commotion  that  but  little  cement  is  said  to  be  lost. 

545.  Other  Methods  of  Depositing  in  Situ.  —  For  deposition 
under  water  the  materials  for  concrete  are  sometimes  mixed 
dry,  but  this  is  not  good  practice.     The  mere  soaking  of  water 
into  cement  does  not  form  a  compact  mortar;  the  moistened 
materials  need  to  be  thoroughly  mixed  and,  if  possible,  rubbed 
together  in  order  to  obtain  perfect  adhesion.     Then,  too,  if  the 
dry  materials  are  lowered  to  place  and  water  is  suddenly  al- 
lowed access  to  the  mass,  much  of  the  cement  will  be  washed 
away  in  the  disturbance  caused  by  the  sudden  inrush  of  water. 

M.  Paul  Alexandre  2  found  by  experimenting  on  mortars  of 
"dry"  (stiff),  "wet"  and  "ordinary  consistency,"  that  mortars 


1  "Subaqueous  Foundations,"   London  Engineering,   1892.     Abstract  in 
Engineering  News,  Vol.  xxviii,  p.  379. 

2  "  Rec.herches  Experimentales  sur  les  Mortiers  Hydrauliques,"  par  M.  Paul 
Alexandre,  pp.  93-96. 


374  CEMENT  AND  CONCRETE 

mixed  "dry"  suffered  the  greatest  decrease  in  strength  by  im- 
mersion in  running  water.  Mortars  mixed  "wet"  suffered  the 
least  loss,  though  their  resistance  was  less  than  those  mixed  to 
the  ordinary  consistency,  since  when  not  subject  to  the  current 
of  water,  the  wet  mortars  gave  much  lower  results  than  those 
of  ordinary  consistency. 

546.  In  order  to  avoid  the  washing,  out  of  the  cement,  the 
concrete  is  sometimes  allowed  to  partially  set  before  deposition. 
Mr.  Robert  W.  Kinipple  has  used  this  method  and  advocates 
its  adoption.1     In  employing  this  method,  the  concrete,  which 
should  be  deposited  when  of  the  consistency  of  stiff  clay,  re- 
quires careful  watching  that  it  does  not  set  so  hard  as  not  to 
reunite   after  being  broken   up.     Under   ordinary   supervision, 
this  will  probably  not  prove  as  successful  as  some  of  the  other 
devices,  but  it  may  be  found  valuable  under  certain  circum- 
stances.    The  writer  made  a  few  experiments  with  this  method 
on  a  small  scale  in  swiftly  running  shallow  water.     Much  of  the 
cement  appeared  to  be  washed  out  by  the   current,   but  the 
results   were   somewhat   better   than   were   obtained   when   the 
concrete  was  deposited  fresh.     (See  §  456.)     M.  Paul  Alexandre 
made  some  short  time  experiments  on  this  point,  which  indi- 
cated  that  but  little  advantage   was  gained  in   allowing  the 
cement  to  partially  set  before  deposition. 

547.  DEPOSITING  CONCRETE  IN  BAGS.—  The  second  method 
of  depositing  concrete  under  water,  namely/by  placing  the  freshly 
mixed  concrete  in  coarse  sacks  and  immediately  lowering  them 
to   place,   is  very  convenient  under  certain   conditions.     This 
method  is  of  especial  value  in  leveling  a  foundation  to  receive 
concrete  blocks,  or  to  form  a  base  for  concrete  deposited  in  situ. 
Small  bags  of  concrete  have  been  successfully  used  in  filling  the 
spaces  between  pile  heads  which  were  to  support  an  open  caisson. 
In  such  a  case  the  bags  should  be  lowered  to  a  diver  who  places 
and  rams  them.     If  the  bags  be  properly  leveled  and  the  earth 
firm,  a  part  of  the  load  is  thus  transmitted  to  the  material  be- 
tween the  pile  heads,  while  if  the  earth  be  very  unstable,  the 
bag  construction  compels  the  piles  to  act  together,  giving  lateral 
stiffness  to  the  foundation  and  tending  to  prevent  over  turning. 


1  "Concrete  Work  under  Water,"  Proc.  Inst.  C.  E.,  Vol.  Ixxxvii.     See 
also  "Notes  on  Concrete,"  by  John  Newman,  pp.  116  and  117. 


PLACING   UNDER   WATER  375 

548.  The   bag    method   was   successfully   used   in   replacing 
with  concrete  the  timber  superstructure  of  the  breakwater  at 
Marquette,   Mich.1     The  main  portion  of  the  breakwater  was 
built  of  monolithic  blocks  on  the  rock-filled  timber  substruc- 
ture.    After  removing  a  portion  of  the  rubble  filling,  a  bed  was 
made  for  the  monolithic  blocks  by  laying  concrete  in  place  two 
feet  thick,    extending  from  one  foot  below  to  one  foot  above 
low   water   datum.     This    method   was   afterward   replaced   by 
the  use  of  concrete  in  bags,  which  made  it  safe  to  remove  a 
lesser  amount  of  the  rock  filling  of  the  crib  at  the  center,  and 
thus  decreased   the  expense  of  the   work.     The  bags   were  of 
eight  ounce  burlap  made  6  feet  long  and  6  feet  8  inches  in  cir- 
cumference, and  held  about  one  ton  of  concrete.     They  were 
filled  while  lying  on  a  skip  specially  constructed,  so  that  when 
the  skip  was  in  place  it  could  be  tripped  and  the  bag  placed  in 
its  exact  position  in  the  work. 

549.  In  connection  with  this  work  a  practical   indication  of 
the   character  of   the   concrete   deposited   in   this   manner   was 
given  by  some  small  bags  of  concrete  that  were  laid  to  protect, 
during  the  winter  storms,   a   portion  of  the   crib   filling.     Mr. 
Coleman   says   of   this,2  "Only  one   layer  of  these  sacks,   laid 
slightly  overlapping  from  the  lake  side  of  the  crib,  was  used. 
The  sacks  were  so  lightly  filled  that  when  laid  as  described,  the 
average  thickness  of  the  concrete  covering  was  not  more  than 
six  inches.     The   crib  was  storm  swept  many   times   without 
displacing  a  single  sack,  and  when  they  were  removed  in  the 
following  spring  to  facilitate  the  work,  they  came  away,  when 
pulled  up  with  the  floating  derrick,  a  dozen  or  more  at  a  time, 
so   firmly   were   they   cemented   together,   and   in   many   cases 
large  rubble  stones  were  lifted  up  along  with  them,  because  of 
the  adhesion  of  the  cement  to  their  surfaces." 

550.  The  Cost  of  the  concrete  in  bags  was  as  follows:  - 

Materials,  cement,  sand,  stone,  burlaps,  etc .$5.281 

Mixing  concrete  and  filling  bags 912 

Transportation 157 

Depositing .408 

Total  cost  per  cubic  yard $6.758 

Or,  cost  in  bags,  exclusive  of  materials     ....      1.477 


Major  Clinton  B.  Sears,  Corps  of  Engineers,  in  charge;  Mr.  Clarence 
Coleman,  Asst.  Engineer. 

J  Report  Chief  of  Engineers,  U.  S.  A.,  1897,  p.  2620. 


376  CEMENT  AND  CONCRETE 

The  cost  of  the  first  plan,  placing  a  two  foot  layer  of  con- 
crete in  situ,  where  different  methods  of  handling  were  em- 
ployed, was,  for  labor:  — 

Loading  scow  with  materials $0.411 

Mixing  concrete 846 

Depositing 524 

Cost  in  situ,  exclusive  of  materials $1.781 

551.  When  concrete  bags  are  used  in  forming  a  foundation, 
the  lower  layers  should  usually  cover  a   considerably  greater 
area  than  that  required  for  the  top.     Especially  is  this  true  if 
building  upon  insecure  earth.     This  increased  area  at  the  bot- 
tom may  be  obtained  by  building  the  sides  on  a  batter,  or  by 
the  use  of  footing  courses.     If  the  latter  are  used,  they  should 
be  so  designed  that  in  any  case  the  projection  beyond  the  course 
next  above  is  not  greater  than  the  thickness  of  the  layer. 

Before  filling  the  concrete  into  the  bags  it  should  be  thor- 
oughly mixed,  as  for  deposition  in  the  ordinary  manner.  The 
practice  of  using  dry  concrete  for  this  purpose  is  reprehensible 
for  the  same  reason  as  has  been  given  in  §  545.  It  has  also  been 
found  that  if  the  concrete  is  mixed  and  filled  into  the  bags  in 
a  dry  state,  a  layer  of  concrete  on  the  outside  may  cake  before 
the  water  has  had  time  to  reach  the  interior  portion.  The 
bags  should  be  filled  about  three-fourths  full,  leaving  the  mass 
free  to  adjust  itself  to  inequalities  in  the  rock,  or  to  the  irreg- 
ular surface  of  the  previously  deposited  layer.  When  strength 
and  compactness  are  desired,  the  bags  should  be  placed  by  a 
diver  and  gently  rammed.  In  this  way  the  mass  may  be  well 
bonded  by  " breaking  joints." 

552.  Large  Masses  in  Sacks.  —  Very  large  bags  of   concrete 
are  sometimes  employed,  as  in  the  construction  of  a  breakwater 
at  New  Haven,  England.1     "The  top  of  the  breakAvater  has  a 
width  of  thirty  feet,  is  ten  feet  above  high  water,  and  is  sur- 
mounted by  a  covered  way  and  parapet  running  along  the  outer 
side,   both   sides   battering   one   in   eight.     The   breakwater   is 
unsheltered  from  the  force  of  the  Atlantic,  is  founded  on  the 
rough,  natural  sea  bottom,   and  the  foundation  course  has  a 


1  From  London  Engineering,   quoted  in  Engineering  News,  Vol.  xxvii, 
p.  551. 


PLACING   UNDER   WATER  377 

width  of  fifty  feet;  the  lower  portion  of  the  structure,  from  the 
bottom  up  to  a  level  of  two  feet  above  low  water,  consists  of 
one-hundred-ton  sacks  of  concrete  deposited  while  plastic. 
The  canvas  with  which  the  concrete  was  enveloped  was  of 
jute,  weighing  about  twenty-seven  ounces  per  square  yard. 
The  sacks  were  dropped  into  place  by  a  specially  designed 
steam  hopper  barge.  The  ' sack-blocks'  in  the  finished  work 
became  flattened  to  a  thickness  of  about  two  feet  six  inches. 
With  the  exception  of  this  sack  work  the  breakwater  is  built 
of  plastic  concrete  laid  in  situ."  Similar  sack-blocks  of  one 
hundred  sixty  tons  have  been  employed  in  breakwater  con- 
struction. 

It  is  evident  that  this  method  of  depositing  concrete  in 
large  sacks  is  peculiarly  suited  to  forming  a  foundation  on  a 
soft  bottom,  since,  if  the  bags  are  made  to  project  well  beyond 
the  sides  of  the  molded  concrete  to  be  deposited  above,  they 
act  in  the  double  capacity  of  a  mattress  to  prevent  scour,  and 
a  foundation  for  the  upper  part  of  the  structure. 

553.  Other  uses     for   Bags  of  Concrete.  —  In  the  construc- 
tion of  the  Merchants'   Bridge  at  St.  Louis,  bags  of  concrete 
were  used  to  check  the  scour  which  occurred  beneath  the  up- 
stream cutting  edge  of  one  of  the  caissons  while  it  was  being 
grounded.     The  bags  were  thrown  into  the  river  at  such  a  dis- 
tance above  the"  pier  that  they  settled  to  the  bottom  at  the 
point  where  the  scour  was  taking  place. 

Burlap  bags  were  used  at  St.  Marys  Falls  Canal  for  laying 
concrete  under  water  next  the  face  of  the  form  to  prevent 
washing  of  the  cement  in  building  concrete  superstructure  for 
canal  walls.  As  the  bags  were  placed  by  hand  they  were  made 
to  hold  only  about  two  cubic  feet  of  concrete. 

554.  Paper  Sacks.  —  Paper   sacks  are  sometimes  employed 
instead  of  jute  bags.     Dr.  Martin  Murphy  1  describes  the  meth- 
ods employed  in  filling  steel  cylinders  for  the  substructure  of 
the  Avon  Bridge  as  follows:  "Bags  made  of  rough  brown  paper 
well  stiffened  with  glucose,  were  employed  and  slipped  into  the 
water  over  the  required  place  of  deposition.     Each  bag  held 
about  one  cubic  foot  of  concrete;  smaller  ones  were  used  be- 


"  Bridge  Substructure  and  Foundations  in  Nova  Scotia,"  by  Martin 
Murphy.    Trans.  A.  S.  C.  E.,  Vol.  xxix,  p.  629. 


378  CEMENT  AND  CONCRETE 

tween  dowels.  The  bags  were  quickly  made  up  and  dropped 
one  after  another,  so  that  the  one  following  was  deposited 
before  the  cement  escaped  from  the  former  one.  The  paper 
was  immediately  destroyed  by  submersion,  and  the  cement 
remained;  it  could  not  escape.  The  bags  cost  one  dollar  thirty- 
five  cents  per  hundred,  or  thirty-five  cents  per  cubic  yard." 
The  success  of  this  method  will  depend  upon  the  character  of 
the  sacks,  for  in  some  experiments  on  a  small  scale  with  sacks 
of  stiff  manila  paper  the  author  found  that  the  bags  were  not 
destroyed,  and  that  no  adhesion  took  place  between  the  separate 
sacks. 

555.  THE  BLOCK  SYSTEM  OF  CONCRETE  CONSTRUCTION.  - 

The  advantage  of  the  block  system  of  construction  lies  in  the 
fact  that  the  individual  blocks  may  be  made  with  the  greatest 
care,  and  as  they  are  allowed  to  harden  thoroughly  before  being 
put  in  place,  the  loss  of  cement  incident  to  the  other  systems 
is  avoided.  There  is,  however,  the  difficulty  of  forming  a  joint 
between  adjacent  blocks.  The  joints  are  of  great  importance 
when  small  blocks  are  employed,  since  the  latter  may  not  have 
sufficient  weight  to  escape  being  washed  out  of  the  work.  Large 
blocks  may  make  a  very  solid  structure  by  being  simply  super- 
imposed, but  special  hoisting  machinery  will  be  required  to 
place  such  blocks. 

Sometimes  a  large  bed  of  mortar  is  laid  in  coarse  sacking 
and  carefully  lowered  and  spread  on  the  block  last  laid,  the 
next  block  being  placed  upon  it  immediately.  A  very  rich 
mortar  should  be  used  for  this  purpose.  Usually,  however,  it 
is  not  attempted  to  place  mortar  in  the  horizontal  joints  in 
concrete  block  work  laid  under  water,  but  it  is  considered  that 
all  vertical  joints  should  be  filled  with  rich  Portland  cement 
mortar  when  the  work  is  to  be  exposed  to  wave  action.  If 
settlement  is  anticipated,  and  large  blocks  are  used,  no  attempt 
should  be  made  to  break  joints  in  the  direction  of  the  longer 
dimension  of  the  work,  but  the  blocks  should  bond  in  a  direc- 
tion transverse  to  the  wall.  Concrete  blocks  may  be  advan- 
tageously employed  to  form  the  faces  of  a  structure  built  under 
water  or  exposed  to  wave  action,  the  concrete  hearting  or 
backing  being  built  in  situ. 

556.  For   convenience   in   handling,   a   groove   to   receive   a 
chain  or  cable  should  be  left  down  two  sides  and  across  the 


PLACING   UNDER   WATER  379 

bottom  of  the  blocks  to  enable  them  to  be  placed  close  together 
and  to  facilitate  the  withdrawal  of  the  hoisting  chain.  These 
grooves  may  afterward  be  filled  with  concrete;  such  recesses 
are  sometimes  molded  for  the  sole  purpose  of  filling  them  with 
fresh  concrete  when  in  place,  and  thus  binding  the  work  to- 
gether. The  molds  for  forming  the  blocks  should  be  carefully 
made  in  order  that  the  finished  blocks  may  have  good  bearings 
one  upon  another.  If  the  corners  are  rounded,  they  are  less 
likely  to  be  chipped  off  in  handling  or  by  having  an  undue 
strain  come  upon  the  corner  when  in  place. 

If  any  recesses  are  desired  in  the  blocks,  the  pieces  placed 
in  the  mold  to  form  them  should  be  trapezoidal  in  cross-section 
with  the  longer  parallel  face  against  the  side  of  the  mold.  If 
such  filling  pieces  are  made  rectangular,  difficulty  will  be  ex- 
perienced in  removing  them  when  the  concrete  has  set.  The 
molds  should,  of  course,  be  so  constructed  as  to  be  readily 
taken  apart  to  be  used  again.  The  opposite  sides  may  be  kept 
from  spreading  by  rods  which  pass  through  the  mold,  but  such 
rods  are  an  inconvenience  in  packing  the  concrete  into  the 
mold,  and  it  is  therefore  better  to  truss  the  mold  outside.  If 
such  tie  rods  are  used,  they  may  be  left  imbedded  in  the  con- 
crete, or  removed  with  the  mold,  as  desired. 

557.  Cost  of  Molding  Blocks.  —  An  illustration  of  the  use  of 
the  block  method  is  furnished  in  the  United  States  breakwater 
at  Marquette.1  The  general  plan  of  this  breakwater  has  already 
been  briefly  noted  and  two  methods  of  laying  a  two  foot  layer 
of  subaqueous  concrete,  as  a  foundation  for  monolithic  blocks 
forming  the  superstructure  proper,  have  been  described.  A 
third  method  was  to  mold  footing  blocks,  seven  feet  by  five  feet 
in  section  and  two  feet  high,  which  were  afterward  laid  flush 
with  the  lake  side  of  the  substructure  cribs  and  filled  in  behind 
with  concrete  laid  in  place.  The  footing  blocks  thus  assured 
a  good  quality  of  concrete  beneath  the  toe  of  the  monolithic 
block  on  the  lake  side  where  it  was  most  necessary  to  provide 
a  good  foundation,  and  also  served  as  a  protection  behind  which 
the  remainder  of  the  two  foot  layer  could  be  placed  with  greater 
facility. 

Many  of  these  blocks  were  built  during  the  winter  in  a  shed 


Report  Chief  of  Engineers,  1897,  p.  2624. 


380  CEMENT   AND   CONCRETE 

artificially  heated,  the  materials  being  thawed  out  as  required. 
The  molds  were  of  six  by  six  inch  and  four  by  four  inch  pine, 
lined  with  two  by  eight  inch  plank  dressed  on  one  side.  Strips 
of  trapezoidal  cross-section,  nailed  inside  the  mold,  provided  for 
two  parallel  grooves  on  the  bottom  and  two  sides  of  the  block 
to  receive  hoisting  chains.  A  dovetail  at  the  back  of  the  block 
was  also  formed  by  three  wedge-shaped  pieces  placed  against 
the  back  face  of  the  mold.  The  cost  per  cubic  yard  of  making 
forty  blocks  is  as  follows:  — 

1.42  bbls.  Portland  cement,  at  $2.75 $3.90 

.45  cu.  yd.  sand,  at  $0.45 20 

1.0  cu.  yd.  stone  screenings  passing  f"  sieve,  at  $1.10,      1.10 

Cost  material  in  concrete  per  cu.  yd $5.20 

Superintendence,  labor  and  watchman $2.21 

Fuel 31 

10  per  cent,  of  cost  of  warehouse  and  molds 52 


Total  cost  of  making  per  cu.  yd 3.04 


Total  cost  per  cu.  yd.  of  blocks  ready  to  place 

in  work $8.24 


CHAPTER  XIX 

CONCRETE-STEEL 

558.  The  ratio  between  the  compressive  and  tensile  strengths 
of  steel  is  nearly  unity.     The  same  thing  is  approximately  true 
of  wood  and  some  other  materials  of  construction.     In  cement 
and  concrete,  however,  the  conditions  are  quite  different,  the 
strength  in  compression  being  from  five  to  ten  times  the  strength 
in  tension.     Concrete  cannot,  therefore,  be  economically  used  to 
resist  tension,  and  in  structures  requiring  transverse  strength 
concrete  is  at  a  great  disadvantage. 

559.  The  idea  of  supplementing  the  tensile  strength  of  con- 
crete by  the  use  of  iron  in  combination  with  it,  seems  to  have 
been   suggested    independently    by    a    number   of    men.     It    is 
known  that  combination  beams  were  tested  by  Mr.  R.  G.  Hat- 
field  as  early  as  1855.     In  1875  Mr.  W.  E.  Ward,1  M.  Am.  Soc. 
Mech.  Engrs.,  constructed  a  dwelling  entirely  of  "beton,"  the 
floors,  roofs,  etc.,  being  reinforced  with  light  iron  beams  and 
rods.     These  early  uses  of  the  combination  have  some  bearing 
upon  the  ability  of  patentees  to  cover  in  their  blanket  patents 
more  than  the  peculiar  form  of  the  steel  member  which  they 
advocate  in  their  particular  system. 

ART.  65.     MONIER  SYSTEM 

560.  A  much  more  picturesque  beginning  of  the  concrete- 
steel  industry  is  furnished  in  the  story,  quite  true*,  that  about 
1876,  a  French  gardener,  Jean  Monier,  used  a  wire  netting  as 
the  nucleus  about  which  to  construct  his  pots  for  flowers  and 
shrubs,   and  seeing  that  the   practice   might  be   extended,   he 
called  to  his  aid  engineers  and  capitalists  who  developed  the 
Monier  system  of  construction. 

This  system  consists  of  imbedding  in  the  concrete  two  sets 
of  parallel  rods  at  right  angles  to  each  other,  the  rods  of  the 
two  sets  being  tied  together  with  wire  at  all  intersections. 


1  Proc.  Am.  Soc.  Mech.  Engrs.,  VoJ .  iv,  p.  388. 

381 


382  CEMENT  AND  CONCRETE 

The  larger  wires  run  in  the  direction  of  the  greater  tensile  stresses 
and  are  usually  spaced  two  to  four  inches  apart.  The  rods  at 
right  angles  to  these  main  tension  members  are  to  assist  in  dis- 
tributing the  stress  to  the  main  members  and  may  be  of  smaller 
diameter. 

The  iron  rods  in  this  system  are  designed  primarily  to  resist 
the  tension  only,  and  the  form  of  the  bars  is  not  such  as  will 
stiffen  the  structure  while  the  concrete  is  fresh.  In  an  arch, 
two  systems  of  netting  are  used,  one  near  the  intrados  and  one 
near  the  extrados. 

561.  The  main  advantages  which  this  system  has  over  some 
of  its  competitors  are  the  simple  shapes  required,  that  is,  round 
rods,   which   may   always  be  obtained   without  difficulty,   and 
the  fact  that  these  may  be  so  readily  put  together  by  ordinary 
workmen  under  supervision.     This  system  is  especially  adapted 
to   vertical  walls,  whether   curved   or   straight,    and   found   its 
first  extensive  use  in  the  construction  of  tanks  and  reservoirs. 
It  has  been  extended,  however,  to  the  construction  of  sewers, 
floors,  roofs,  and  arch  bridges. 

One  of  the  practical  disadvantages  of  the  system  is  that  the 
nets  are  somewhat  difficult  to  handle  and  keep  in  position,  and 
in  thin  sections  it  has  not  been  found  practical  to  imbed  the 
nets  in  concrete  containing  broken  stone  of  the  ordinary  size. 
The  use  of  cement  mortar,  usually  one  part  cement  to  three 
sand,  has  been  found  necessary  in  order  to  get  a  perfect  con- 
nection between  the  wires  and  the  body  of  the  work.  This, 
of  course,  increases  the  cost.  Another  objection  has  been 
urged  against  it,  namely,  that  the  transverse  rods  do  not  in 
general  have  any  ^duty  to  perform,  and  are  simply  a  waste  of 
material  so  far  as  the  final  strength  of  the  structure  is  con- 
cerned. While  this  may  be  so  in  certain  forms  of  construction, 
it  may  be  met  by  the  statement  that  these  cross-rods  may  be 
made  as  small  as  desired  if  they  are  to  act  merely  as  spacers 
for  the  main  rods.  In  slabs,  walls,  etc.,  however,  these  cross- 
rods  have  a  purpose,  and  in  some  other  systems  members  are 
supplied  to  fulfill  this  necessary  function. 

562.  Some  very  bold  arches  have  been  built  on  the  Monier 
system,  including  three  bridges  in  Switzerland  having  128  foot 
span,  11  foot  rise,  and  a  thickness  of  but  6|  inches  at  the  crown 
and  10  inches  at  the  abutments. 


PATENTED  SYSTEMS  383 

A  Moriier  arch  of  32.8  foot  span,  rise  one-tenth  of  span, 
width  13.2  feet,  in  which  the  mortar  at  the  crown  was  six  inches 
thick  and  eight  inches  at  the  abutments,  was  tested  in  Austria 
in  1890.  It  held  a  fifty-three  ton  locomotive  on  half  the  arch, 
and  finally  failed  at  the  abutments  under  a  load  of  1,700  pounds 
per  square  foot  over  half  the  span. 

563.  Pipes  are  now  made  by  this  system  at  yards  and  trans- 
ported to  the  place  of  use.     It  has  also  been  used  as  a  substi- 
tute for  iron  in  cylinders  for  bridge  piers.     A  novel  use  of  this 
system  consists  in  making  a"  pipe  covering  for  piles  exposed  to 
marine  borers.     The  pipe,  which  is  long  enough  to  reach  from 
above  the  water  surface  to  below  the  bed  of  the  waterway,  is 
slipped  over  the  head  of  the  pile  and  settled  a  short  distance 
into  the  mud  or  silt  of  the  bottom  with  the  aid  of  a  water  jet. 
A  question,  however,  has  been  raised  as  to  the  action  of  con- 
crete and  iron  in  combination  in  sea  water  on  account  of  the 
possible  setting  up  of  galvanic  action. 

ART.  66.     WUNSCH,  MELAN,  AND  THACHER  SYSTEMS 

564.  Wiinsch  System. — This  system,   which   was    invented 
in   1884  by  Robert  Wiinsch  of  Hungary,  consists  of  two  iron 
members  of  angle  irons  and  plates  imbedded  in  concrete,  the 
lower  member  being  arched  and  conforming  to  the  outline  of 
the  soffit,   while  the  upper  one  is  horizontal  and  continuous. 
The  two  members  are  riveted  together  at  the  crown,  and  at  the 
abutment   are   rigidly   connected   by  a   vertical   member.     The 
several  systems  of  rib  bracing  thus  constructed  are  connected 
laterally  at  the  abutment  by  channel  bars  running  transverse 
to  the  arch  and  riveted  to  the  bottom  of  each  vertical  in  the 
abutment.     Assuming  that  the  abutments  are  stable,  it  is  evi- 
dent that  we  have  here  not  simply  an  arch,  but  also  some  ele- 
ments of  the  cantilever.     The  spandrels  being  built  up  solid  of 
concrete,   there  is  no   definite  arch  ring,   and  the  quantity  of 
material  required,  especially  in  long  spans,  is  likely  to  be  much 
greater  than  in  other  systems.     On  the  other  hand,  the  great 
depth  at  the  springing  permits  the  use  of  concrete  only  moder- 
ately rich  in  cement. 

565.  A  bridge  of  this  type,  built  at    Neuhausel,   Hungary, 
consists  of  six  spans  of  about  56  feet  each,  rise  3.7  feet,  thick- 
ness  at  crown  9.8  inches,   and   at  springing  line  54.3  inches. 


384  CEMENT  AND  CONCRETE 

The  total  width  of  the  arch  was  19.7  feet  and  contained  thir- 
teen systems  of  arch  ribs.  Concrete  in  the  abutments  below 
water  was  made  mainly  of  Roman  cement.  Above  water  it 
was  composed  of  one  part  Portland  to  eight  or  ten  parts  sand 
and  gravel.  Ten  to  twelve  inches  of  the  arch  was  built  of 
strong  Portland  concrete  rammed  in  layers  at  right  angles  to 
radial  lines  of  the  arch,  special  care  being  taken  with  that  part 
below  the  bottom  arched  member.  An  arch  was  usually  com- 
pleted in  one  day,  and  the  centers  remained  in  place  thirty  to 
forty  days,  the  greatest  settlement  on  the  removal  of  centers  being 
two-thirds  of  an  inch.  This  bridge  contained  1,346  cubic  yards  of 
concrete  and  88,180  pounds  of  iron,  and  cost,  complete,  $13,700. 

566.  Melan  System.  —  This  system,  invented  by  an  Austrian 
engineer,  Joseph  Melan,  consists  of  arched  ribs  between  abut- 
ments as  in  bridges,  or  between  beams  or  girders  as  in  floor 
construction,  the  space  between  the  ribs  being  filled  with  con- 
crete.    Steel   I-beams  curved  to  the  proper  form  are  usually 
employed  for  the  reinforcement,  though  angle  iron  flanges  with 
lattice  connections  have  been  used  in  some  of  the  large  bridges. 
The  steel  members  extend  into  the  piers  or  abutments  and  are 
there  connected  by  angles  or  other  shapes,  and  firmly  imbedded 
in  the  concrete. 

567.  This   system   as   adapted    to   bridge    construction   has 
probably   met   with   greater  favor   among   American   engineers 
than  any  other  form.     Perhaps  this  is  because  of  the  stiffness 
of  the  form  of  iron  beam  used,   and  because  by  assuming  a 
rather  high  fiber  stress  for  steel  the  reinforcement  may  be  de- 
signed to  withstand  the  entire  bending  moment  without  exces- 
sive dimensions  for  the  steel  members.     There  is  thus  a  feeling 
of  security  in  its  use  that  is  not  felt  in  the  same  degree  with 
other  systems.     The  arch  dimensions  are  determined  by  com- 
puting  the   forces   and   required   thickness   of   arch   ring   after 
assuming  certain  safe  working  stresses  for  the  steel  and  con- 
crete; but  if  desired,  the  size  of  steel  members  may  then  be 
increased    slightly    where   necessary   to    such   dimensions   that 
with  unit  stresses  of,  say,  one-half  the  elastic  limit,  the  entire 
bending   moment  shall   be  taken   by   the  steel.     Some  of   the 
largest  bridges  built  after  this  system  in  the  United  States  are 
the  five-span  bridge  at  Topeka,  Kan.,  and  the  three-span  bridge 
at  Paterson,  N.  J. 


PATENTED  SYSTEMS  385 

568.  Thacher  System.  —  A  modification  of  the  Melan  system 
is  that  invented  and  patented  by  Mr.  Edwin  Thacher.     Steel 
bars  are  used  in  pairs  and  imbedded  in  the  concrete  near  the 
intrados  and  extrados  of  the  arch  and  extending  well  into  the 
abutments.     The  bars  of  each  pair  may  be  connected  by  bolts 
or  stirrups,   though    Mr.  Thacher's  original  idea  seems  to  have 
been  to   have  no   connection  between    two  bars  of  a   pair  ex- 
cept  through   the   concrete.     The  bars   are   provided  with  pro- 
jections   which  may    be    in    the    form  of    rivet   heads,  lugs,  or 
bolts,  to  increase  the  resistance  of   the  bars  to  slipping  in  the 
concrete. 

569.  Mr.  Thacher  has  more  recently  designed  a  special  form 
of  rolled  bar  having  projections  that  serve  the  same  purpose 
as   the   rivet   heads    mentioned    above.     Several   bridges   have 
been  built  on  this  system,  one  of  the  most  notable  of  these  being 
the  Goat  Island  bridge  at  Niagara  Falls,  one  span  of  which  is 
110  feet  in  length. 

570.  In  the  construction  of  arch  bridges  many  of  the  other 
systems  are  simply  modifications  of  the  Melan.     The  shapes  of 
the  steel  members  may  have  different  forms,  and  the  connec- 
tions between  the  pairs  of  bars  forming  the  arch  ribs  may  vary 
to  suit  the  idea  of  the  inventors.     But  though  these  systems 
lose  their  identity  in  long-span  arches,  their  distinctive  features 
are  more  apparent  in  the  construction  of  floors,  roofs,  columns, 
etc. 

ART.  67.     OTHER  SYSTEMS  OF  CONCRETE-STEEL 

571.  The  Hennebique  System.  —  The  rods  are  here  arranged 
in  pairs,  one  above  the  other,  in  a  vertical  plane.     In  girders, 
the  bar  in  the  tension  side  is  straight,  while   the  other  one  of 
the  pair  is  horizontal  for  a  short  distance  along  the  center  of  the 
span,  the  ends   being   inclined    upward   near   the    ends  of   the 
beam.     The  two  bars  are  connected  by  bent  straps  or  U-bars 
so  that  the  steel  reinforcement  may  be  compared  to  a  queen 
post  truss  within  the  concrete.     This  system  has  been  used  in 
the  construction  of  bridges,  both  arch  and  girder,  floors,  roofs, 
stairways,  etc.,  but  it  is  in  beams  and  girders  that  its  distin- 
guishing characteristics  are  best  displayed. 

572.  A  beautiful  arch  on  this  system  is  the  bridge  over  the 
river  Vienne  at  Chatellerault,  France,  consisting  of  three  spans, 


386  CEMENT  AND  CONCRETE 

the  central  one  of  which  is  164  feet  long,  with  rise  of  15  feet, 
8  inches.  Four  arch  ribs  20  inches  deep  .support  the  roadway, 
25  feet  wide,  by  posts  forming  a  skeleton  spandrel. 

573.  Kahn   System.  —  In   this   system,   which   is   somewhat 
similar  to  the  Hennebique,  the  distinguishing  feature  is  the  care 
taken  to  provide  against  shear,  or  against  that  combination  of 
tension  and  shear  which  tends  to  cause  failure  in  a  beam  by 
cracks   that  extend   diagonally   upward   toward   the   center   of 
•span  from  near  the  points  of  support.     The  steel  plates  forming 
the   tension  members   are  sheared  longitudinally   at  intervals, 
and  short  ends  are  bent  up  at  an  angle  of  forty-five  degrees 
with  the  horizontal.     These  ends,  which  may  be  compared  to 
the  tension  diagonals  of  a  truss,  are  thus  a  part  of  the  main 
steel    member,    and   the   stress   is   transferred    directly   to    the 
latter  without  dependence  on  the  concrete. 

The  advantages  are  the  great  resistance  offered  by  the  bar 
to  being  pulled  out  of  the  concrete  and  the  thorough  manner 
in  which  all  tension  stresses  may  be  provided  against.  The 
main  disadvantages  would  seem  to  be  the  necessity  of  detailed 
shop  work  for  each  size  of  girder,  the  inconvenience  of  shipping 
the  steel  in  its  complete  form  and  the  difficulty  of  thoroughly 
tamping  the  concrete  around  the  diagonals. 

574.  The  Ransome  System.  —  One  of  the  earliest  patents  to 
be  issued  in  this  country  for  a  method  of  using  concrete  and 
iron  in  combination  was  that  issued  to  Mr.  E.  L.  Ransome  in 
1884.     The  valuable  and  distinctive  feature  of  this  system  is 
the  use  of  a  square  bar  that  has  been  twisted  cold.     This  twist- 
ing not  only  insures  a  good  bond  between  the  concrete  and  iron, 
but  actually  somewhat  increases  the  strength  of  the  bar. 

In  building  beams  with  twisted  bars  as  tension  members,  the 
latter  are  given  a  slight  inclination  from  the  center  upward 
toward  the  ends.  For  use  in  buildings,  as  in  floors  and  columns, 
and  for  covers  to  areaways,  and  similar  uses,  this  system  is 
largely  employed. 

575.  Roebling  System.  —  As    its  name  implies,   wire  forms 
the  main  feature  of  this  system,  and  in  a  general  way  it  resem- 
bles the  Monier.     Its  application  thus  far  is  found  principally 
in  floor  construction,  two  distinct  methods  being  used.     In  the 
arched  floor  a  wire  netting,  stiffened  by  round  steel  rods  woven 
through  it    is  sprung  between  the   lower  flanges   of   the    main 


STRENGTH  387 

I-beams  of  the  floor.  This  netting,  further  stiffened  and  held  in 
place  by  iron  rods  running  parallel  to  the  axis  of  the  arch,  forms 
a  permanent  center  for  the  placing  of  the  concrete,  which  fills 
all  of  the  space  to  the  level  of  the  top  of  the  I-beams.  A  level 
veiling  below  is  obtained  by  a  similar  netting  laid  flat  against 
the  under  side  of  the  I-beam  and  fastened  thereto.  This  acts 
as  a  wire  lath  to  receive  a  coat  of  plaster.  If  the  level  ceiling 
is  not  necessary,  the  plaster  may  be  applied  to  the  under  side 
of  the  arch  netting,  in  ..which  case  the  lower  flange  of  the  I- 
beam  should  be  encased  in  concrete  to  protect  it  from  corrosion 
and  fire. 

576.  For  lighter  loads,  flat  bars  are  placed   at  suitable  in- 
tervals above  and  below  the  I-beams  and  clamped  to  the  flanges. 
To  these  bars  the  wire  netting  is  attached,  a  thin  layer  of  con- 
crete laid  on  the  upper  wire  incasing  the  bars,  and  plaster  ap- 
plied to  the  lower  netting  forming  the  ceiling.     Cinder  concrete 
is  usually  employed  with  this  system. 

577.  Expanded  Metal.  —  The  use  of  whac  is  commonly  known 
as  expanded   metal  lath   has  been  extended   to    concrete-steel 
construction.     As   in   the    Monier   and    Roebling   systems,    the 
strength  and  stiffness  of  the  structure  are  increased  by  the  use 
of  steel  rods  in  connection  with  the  expanded  metal,  the  chief 
duty  of  the  latter,  where  great  strength  is  required,  being  that 
of    a    distributing    member.     Expanded    metal    is    made    from 
sheet  steel  by  shearing  short  slits  parallel  to  the  grain,  and 
extending  the  sheet  at  right  angles  to  the  slits,  resulting  in  a 
network  o£  diamond  shaped  openings.     The  metal  used  is  of  all 
weights  up  to  one-quarter  inch  thick  with  meshes  six  inches  long. 

578.  The  steel  bars  used  in  connection  with  expanded  metal 
by  the  St.  Louis  Expanded  Metal  Fireproofing  Co.  are  square, 
with  frequent  corrugations  surrounding  the  bar.     These  corru- 
gations serve  only  to  prevent  the  slipping  of  the  bars  in  the 
concrete  without  adding  to  the  strength. 

The   applications   of  this  system   include   conduits,   sewers, 
and  walls  of  buildings,  as  well  as  floors  and  roofs. 

ART.  68.     THE  STRENGTH  OF  COMBINATIONS  OF  CONCRETE  AND 

STEEL 

579.  While  we  have  in  this  country  been  somewhat  slow  in 
acknowledging  the  worth  of  concrete-steel   construction,  there 


388  CEMENT  AND  CONCRETE 

is  now  a  strong  interest  displayed  in  the  subject;  many  experi- 
ments are  being  made  in  our  educational  and  commercial  labo- 
ratories and  the  theory  of  the  action  of  concrete  and  steel  in 
combination  is  being  rapidly  developed.  It  is  natural  that  in 
the  investigation  of  a  form  of  construction  permitting  so  many 
variations  in  methods  of  preparation,  that  the  opinions  now 
advanced,  based  on  insufficient  data,  should  be  more  or  less 
conflicting. 

580.  Experiments.  —  The  experiments  of   M.   A.   Considere, 
made  in  France  between  1898  and  1901,  which  have  been  made 
more  available  to  us  through  the  translation  and  collection  oi 
his  articles  on  the  subject  by  Mr.   Moisseiff,1  are  exceedingly 
valuable.     The  effect  of  the  quality  of  the  steel  and  the  con- 
crete,  of  repeated  loads,   of  changes  in  volume  in  hardening, 
and  many  other  points  are  carefully  analyzed  by  experiment 
and  theory. 

One  of  the  most  important  deductions  drawn  by  M.  Con- 
sidere is  that  fibers  of  concrete  within  what  may  be  called  the 
sphere  of  influence  of  a  reinforcing  rod  of  iron  or  steel,  is  capable 
of  enduring  very  much  greater  elongations  without  visible  frac- 
ture than  similar  concrete  without  reinforcement.  The  expla- 
nation advanced  for  this  is  that  the  steel  so  distributes  the 
stress  throughout  the  length  of  the  concrete  in  tension  that 
the  development  of  insipient  fractures  or  excessive  elongations 
at  the  weaker  sections  of  the  concrete  is  prevented  until  each 
section  has  taken  its  maximum  load.  The  conclusion  to  which 
this  theory  leads  is  that  the  resistance  of  the  concrete  through- 
out the  area  of  influence  of  the  steel  reinforcement,  is  main- 
tained far  beyond  that  degree  of  deformation  which,  in  concrete 
not  reinforced,  would  cause  its  rupture. 

581.  Neglect  of   Tensile    Strength.  —  Notwithstanding  these 
conclusions,  it  is  believed  that  it  is  sufficient  in  most  cases  of 
design  to  neglect  the  tensile  strength  of  the  concrete  in  concrete- 
steel  combinations.     This  course  may  be  defended  by  the  fol- 
lowing considerations.     The  tensile  strength  of  concrete  is,  at 
best,  not  usually  above  two  hundred  to  four  hundred  pounds 
per  square  inch.     If  the  stress  on  the  extreme  fibers  of  a  beam 


1  "  Reinforced  Concrete,"  by  Armand  Considere,  McGraw  Publishing  Co., 
New  York. 


STRENGTH  389 

is  three  hundred  pounds,  and  we  consider  that  this  stress  de- 
creases uniformly  toward  the  neutral  axis,  the  mean  stress  is 
but  one  hundred  fifty  pounds  per  square  inch.  Again,  if  we 
disregard  M.  Considered  conclusions,  we  find  that  since  the 
modulus  of  elasticity  of  steel  is,  say,  fifteen  times  that  of  con- 
crete, the  former  is  only  stressed  to  forty-five  hundred  pounds 
per  square  inch  when  the  imbedding  concrete  has  reached  its 
ultimate  strength. 

582.  The  resistance  of    concrete  to  tension  may  easily  be 
destroyed  or  impaired  by  accident,  especially  when  fresh.     The 
properties  of  concrete  vary  so   much  with  the  materials,   the 
proportions,   and   the   manipulation,   and   the   investigation   of 
the  behavior  of  concrete  and  steel  under  stress  is  as  yet  so  in- 
complete, as  to  make  refinements  in  theoretical  treatment  not 
only  unwarranted  but  really  undesirable  for  practical  purposes, 
since  they  lead  to  the  appearance  of  greater  accuracy  than  is 
in  reality  attainable. 

It  is  true  that  by  the  judicious  selection  of  values  for  the 
constant  appearing  in  formulas  for  the  strength  of  concrete- 
steel  beams,  the  results  of  such  formulas  sometimes  show  a  re- 
markable agreement  with  the  results  of  that  series  of  actual 
tests  for  which  the  constants  have  been  selected;  but  one  has 
only  to  recall  his  experience  in  other  lines,  hydraulics  for  in- 
stance, to  realize  the  importance  of  the  almighty  constant. 
The  opinion  sometimes  advanced,  that  the  strength  of  a  given 
concrete-steel  beam  may  be  as  accurately  derived  by  formula 
as  can  the  strength  of  a  steel  beam,  the  writer  does  not  believe 
to  be  tenable,  at  least  in  the  present  state  of  our  knowledge 
concerning  the  behavior  of  concrete. 

583.  To   neglect  the  tensile  strength  of    the   concrete   will 
result  in  a  slight  increase  in  the  required  area  of  steel  reinforce- 
ment, and,  in   so  far  as  the  tensile  strength  of  the  concrete 
may  be  developed,  will  tend  to  make  the  compression  side  of 
the  beam  weaker  than  the  tension  side.     The  only  objection 
to   this  is   that   the    failure   of   the  beam,  though  at  a  higher 
load,  may  be   more   sudden.     This  possibility,  however,  seems 
less  serious  than  the  error  of  depending  on  the  tensile  strength 
of  the  concrete    only   to    find   it   lacking    at    the    critical    mo- 
ment. 

Since  the  aim  here  is  to  develop  a  formula  that  may  be  used 


390  CEMENT  AND  CONCRETE 

with  safety  in  the  design  of  structures,  and  since  to  neglect 
the  tensile  strength  of  the  concrete  is  to  add  an  unknown, 
though  probably  small,  factor  of  safety,  the  tensile  strength 
will  not  be  considered  in  the  following  analysis. 

ART.  69.     CONCRETE-STEEL  BEAMS  WITH  SINGLE 
REINFORCEMENT 

584.  Definitions.  —  In  this  discussion  the  word  strain  has 
its  technical  meaning,  the  relative  change  in  length  of  a  piece 
under  stress.  It  is  usually  expressed  as  the  ratio  of  the  elonga- 
tion (or  shortening  if  in  compression)  to  the  original  length  of 
the  piece.  But  for  our  purpose  it  is  the  ratio  of  the  increment 
of  change  in  length,  occasioned  by  a  given  increment  of  stress, 
to  the  length  of  the  piece  before  the  increment  of  stress  was 
applied.  These  two  expressions  for  strain  are  usually  consid- 
ered equivalent,  since,  according  to  Hooke's  law,  the  ratio  be- 
tween stresses  and  corresponding  strains,  for  a  given  material, 
is  constant  within  the  elastic  limit.  But  in  dealing  with  con- 
crete it  is  found  that,  even  before  the  stresses  become  excessive, 
Hooke's  law  does  not  hold  true.  Bearing  in  mind,  then,  the 
meaning  of  the  word  strain,  we  represent  as  usual  the  ratio  of 
stress  to  strain  by  E,  the  modulus  of  elasticity,  or 

^  _  stress 
strain 

Let  Ea  =  modulus  of  elasticity  of  steel. 

Ec  =  modulus  of  elasticity  of  concrete  in  compression. 
/„  =  tension  in  steel,  fbs.  per  sq.  in. 
/   =  compression  in  concrete,  Ibs.  per  sq.  in. 
a  =  thickness  of  steel  considered  as  a  flat  plate,  or  the  area  of  imbedded 

steel  bars  per  inch  of  width  of  beam  z. 
yi  =  distance  the  extreme  fiber  of  concrete  in  compression  is  from  the 

neutral  axis. 
2/2  =  distance  the  center  of  the  steel  reinforcement  in  the  tension   side 

of  the  beam  is  from  the  neutral  axis. 
i    =  depth  of  concrete  below  reinforcement. 
d    =  y\  +  7/2  and  h  =  d  +  i. 

Xi  =  unit  compression  of  extreme  fibers  of  concrete  in  compression, 
X2  =  unit  elongation  of  steel  in  tension. 

Tjl  £ 

Represent  —  by  R,     and     £  by  r. 

&c  fc 


SINGLE  REINFORCEMENT 


391 


585.  Formulas  for  Constant  Modulus  of  Elasticity. — The 
cross-section  of  the  beam,  the  graphical  representations  of  the 
strains  and  of  the  stresses  are  shown  in  the  following  diagrams: 


FIG.  10. 
CROSS-SECTION. 


STRAINS 


FIG.  13. 
STRESSES. 


Figure  12  shows  the  conditions  when  the  stresses  are  so  small 
that  the  modulus  of  elasticity  of  the  concrete  may  be  considered 
constant,  and  this  case  will  be  first  considered. 

In  the  strain  diagram,  At  represents  the  deformation  of  the 
extreme  fiber  of  concrete  in  the  compression  side  of  the  beam, 
and  Ag  the  deformation  of  the  steel.  Since  a  section  plane  be- 
fore bending  is  considered  to  be  plane  after  bending,  the  steel 
is  considered  not  to  slip  in  the  concrete,  and  NN  is  the  neutral 
axis, 

r^  =  — ;     but    Et  =  ~,     and 

^2        2/2  A.2 


r  -  f- 

LJC    x 


or 


and 


A.J  =  ^     and     A!  = 

1          _    »/l        ^    /C      •*-''* 

fc      &s  ft 


(Eq.  1.) 


In   the  stress   diagram   the   triangle   NAB    represents   the 
total  compressive  stress  on  the  concrete  for  unit  width  of  beam, 

and  is  equivalent  to  a  single  force  i^H.  applied  at  the  center  of 

gravity  of  the  triangle. 

The  total  compressive  stress  for  section  of  width  z  is 


The  total  tension  in  the  steel  is  T  =  zafs. 


392  CEMENT  AND  CONCRETE 

As  we  disregard  the  tensile  strength  of  the  concrete,  and  as  the 
total  normal  compression  and  total  normal  tension  on  a  section 
must  be  equal,  as  they  are  the  two  forces  of  a  couple,  we  have 

P  =  T,     or     z^fc=zaf,, 
whence  a  =  £  f  =  f^-  (Eq.  2.) 

Js      4  ^f 

2 

The  point  of  application  of  the  force  P  is  -  yl  above  the  neu- 

o 

tral  axis,  while  the  point  of  application  of  T  is  y2  below  the 

(9  \ 

^    ?/l  +  2/2), 

and  the  moment  of  resistance  is  equal  to  either  force  into  this 
arm, 

H.r*.  + 


substituting  the  value  of  y2  given  in  (1)  and  reducing, 

(Eq-3-> 


586.  Formulas  for  Varying  Modulus  of  Elasticity.  —  The  fore- 
going formulas  are  based  on  the  supposition  that  the  compres- 
sive  stress  in  the  extreme  fiber  of  the  concrete  has  not  passed 
the  point  beyond  which  equal  increments  of  stress  no  longer 
produce  equal  increments  of  strain  or  deformation.  They  are 
based,  in  other  words,  on  the  common  theory  of  flexure,  except 
so  far  as  we  have  departed  from  the  application  of  this  theory 
in  neglecting  the  tensile  strength  of  the  concrete.  It  is  well 
known  that  even  for  steel  and  wooden  beams  this  common 
theory  does  not,  and  is  not  meant  to,  apply  outside  the  elastic 
limit.  In  the  case  of  concrete,  however,  it  has  been  found  that, 
even  for  quite  moderate  stresses,  the  modulus  of  elasticity  is 
not  constant  (Art.  56),  but  that  after  a  certain  stress  is  reached 
the  modulus  decreases  with  increasing  stress.  The  effect  of 
this  upon  the  internal  forces  may  be  illustrated  by  the  curve 
N  B  in  Fig.  13.  The  extreme  fiber  is  supposed  to  be  subjected 
to  the  stress  fc;  the  fibers  nearer  the  neutral  axis  have  a  smaller 
stress  per  square  inch,  and  the  modulus  of  elasticity  for  this 
smaller  stress  is  greater;  but  in  order  that  a  section1  that  is 


SINGLE  REINFORCEMENT  393 

plane  before  flexure  shall  be  plane  after  flexure,  the  strain  must 
be  proportional  to  the  distance  from  the  neutral  axis.  It  fol- 
lows, then,  that  the  stresses  in  the  inner  fibers  do  not  decrease 
accord'  ng  to  the  ordinates  of  the  triangle,  but  are  greater  than 
indicated  by  such  ordinates.  The  exact  form  cf  the  curve 
B  N  is  not  known,  but  the  examination  of  a  number  of  de- 
formation curves  has  indicated  that  it  is  parabolic,  and  for  the 
purpose  of  this  discussion  it  may  be  considered  a  parabola 
with  axis  A  B  without  serious  error,  although  it  is  known  the 
axis  does  not  coincide  with  A  B  for  stresses  below  the  elastic 
limit  of  the  concrete. 

587.  While  the  formulas  derived  in  §585  may  representation, 
the  conditions  existing  in  a  beam  subjected  to  very  moderate 
stresses,  it  appears  that  beyond  the  limit  of  stress  at  which 
the  modulus  of  elasticity  of  concrete  becomes  variable,  they 
should  be  so  modified  as  to  take  into  account  this  variable 
modulus. 

Then  if  A  B  in  Fig.  13  now  represents  fc  and  MS  =  /„,  we  have 
as  before, 


The  total  stress  on  the  concrete  above  the  neutral  axis  is 

2 
now  represented  by  the  area  within  the  parabola,  or     fc  j/lt  and 

the  total  compression  on  section  of  width  z  is 


and  the  total  tension 

Tr  =  zal. 
As  these  are  the  two  forces  of  a  couple 

3  22/i/c  =  z«/8; 
whence  a  =  |  =  |  &..  (Eq.  5.) 


The  point  of  application  of  P'  is  on  a  line  through  the  center 

5 
of  gravity  of  the  parabola,  or  -  y^  from  the  neutral  axis,  while 

o 

the  point  of  application  of  T'  is  at  distance  ?/2  below  the  neutral 


394  CEMENT  AND  CONCRETE 

axis;  the  arm  of  the   couple  is,   therefore,   ^  yl  +  yz,  and  the 

o 

moment  of  resistance 

2 


=   ^  '+?£/ 

Substitute  value  of  yz  given  in  (4) 

59  f       77 

. .f  .    <>.    i    ^  ..£  ..    /«     **e 


In  applying  these  formulas,  it  must  be  remembered  that 
(1),  (2),  and  (3)  are  applicable  where  the  stresses  are  below 
the  point  at  which  the  modulus  of  elasticity  of  the  concrete 
begins  to  diminish,  while  (4),  (5),  and  (6)  illustrate  the  con- 
ditions for  stresses  above  that  limit. 

588.  Example.  —  Design  a  beam  of  10  foot  span  to  carry  a 
load  due  to  20  feet  head  of  water. 

Load  per  square  foot  =  20  X  62.5#  =  1250#. 
Total  load  per  foot  width  of  beam  =  125,000#  =  W^ 
First,  using  Eqs.  1,2,  and  3. 

M  =  ~  =  187,500  inch-lbs.  on  beam  1  ft.  wide,  (z  =  12). 

o 

Assume 

/,  =  12,500,     fe  =  500,     r  =  fs  =  25; 

/c 
'  ft1  ' 

Ea  =  28,000,000,     Ec  =  2,000,000,     R  =  ~  =  14. 
From  (3) 

M0  =  187,500  =  12  X  500       + 


y*  =  25.5,        2/t  =  5.05  inches. 
From  (2) 


az  =  .101  X  12  =  1.21  sq.  in.  of  steel  for  beam  12  in.  wide. 


SINGLE  REINFORCEMENT  395 

From  (1) 

r  25 

7/2  =  -=  v/j  =  -  7  X  5.05  =  9.02  inches, 
it 

If  i  =  thickness  of  concrete  below  center  of  steel  bars  =  2  inches, 
k  =  total  depth  beam  =  5.05  +  9.02  -f-  2.00  =  16.07  inches. 

Second,  using  Eqs.  4,  5,  and  6. 
Assume 

/.  =  50,000,     fe  =  2,000,     r  =  '-  =  25; 

Jc 

Es  =  28,000,000,     Ec  =  1,400,000,     R  =  ('  =  20. 

1C 

As  the  stresses  per  square  inch  given  above  are  approxi- 
mately the  breaking  strengths  of  the  materials,  we  must  supply 
a  factor  of  safety,  say  4;  i.e.,  design  the  beam  to  withstand  four 
times  the  required  bending  moment  before  the  stresses  assumed 
above  are  attained.1 
From  (Eq.  6) 

M0  =  4  M  =  4  X  187,500  =  1 2  X  2000  (^  +  |  X  ?j 

whenc  2  _  187,500  X  4  x  12  _ 

'  y*  '      12  X  2000  xl5~ 

or,  yv  =5. 

From  (Eq.  5) 

2    5 
a  =  3  25  =  '133  inch) 

and        az  =  1.6  square  inches  of  steel  for  12-inch  width  of  beam. 

1  The  method  of  using  the  breaking  strengths  of  the  materials,  and  com- 
puting the  ultimate  resistance  equal  to  a  certain  number  of  times  the  desired 
strength,  is  considered  inferior  to  that  of  assuming  safe  working  stresses  and 
computing  directly  the  safe  load.  These  safe  working  stresses  should  be 
fixed  with  reference  to  the  elastic  limit  of  the  materials,  rather  than  with 
reference  to  ultimate  strength.  The  use  here  of  the  term  factor  of  safety  is 
for  the  momentary  purpose  of  emphasizing  the  fact  that  the  conditions 
assumed  in  deriving  equation  (6)  are  such  as  are  supposed  to  exist  under 
comparatively  high  stresses;  but  the  formulas  may  evidently  be  applied  to 
the  safe  working  stresses  the  same  as  equations  (1),  (2)  and  (3),  and  in  the 
present  example  the  same  size  beam  will  result  by  eliminating  "factor  of 
safety"  and  using  working  stresses  equal  to  one-fourth  the  values  of  the 
stresses  assumed. 


396  CEMENT  AND  CONCRETE 

From  (Eq.  4) 

7*  25 

2/2  =  ft-Ui  =  go  t/i  =  L25  x  5"  =  6'25  inches- 

If         i  =  2  inches  as  before, 

h  =  total  depth  beam  =  5.00  +  6.25  +  2.00  =  13.25  inches. 

It  is  seen  that  equations  4,  5  and  6  give,  for  the  assumption 
made,  a  lesser  depth  of  beam  with  more  reinforcement  than 
is  given  by  equations  1,  2  and  3  with  the  corresponding  as- 
sumptions as  to  stresses  and  moduli. 

589.  An  inspection  of  the  equations  shows  that  to  increase 
the  amount  of  steel  reinforcement  in  the  tension  side  of  the 
beam  tends   to   move   the   neutral   axis   nearer  to   the  tension 
side,  and  bring  a  greater  area  of  cross-section  of  concrete  into 
compression.     If  we  arbitrarily  decrease  the  depth  of  the  beam 
which  must  withstand  the  same  bending  moment,  it  will  in- 
crease the  required  area  of  reinforcement,   and  if  carried  too 
far  will  eventually  raise  fc  beyond  a  safe  value.     On  the  other 
hand,  if  we  take  the  beam  as  designed  in  accordance  with  equa- 
tions 1,  2  and  3  and  subject  it  to  a  greater  bending  moment 
than  that  for  which  it  is  designed,  then  so  long  as  R  remains 
constant,  r  also  remains  constant,  that  is,  the  steel  and  con- 
crete are  equally  overstressed ;  but  since  R  increases  with  the 
load,  r  will  also  increase,   that  is,   the  increment  of  stress  in 
steel  will  be  relatively  greater  than  that  in  concrete. 

590.  Excessive  Reinforcement.  —  In  the  solution  of  the  above 
example  if  we  introduce  the  requirement  that  the  total  depth 
of  the  beam  shall  be  but  12  inches,  while  the  quality  of  the  con- 
crete   is    not    improved,   we     may     assume,   as   before,  Es     — 
28,000,000  and  Ec  =  1,400,000.      Let   us   introduce   the  same 
factor  of  safety,  4,  by    using   fe  =  £-°¥°-°-  =   500  pounds  instead 
of    designing    the   beam    for   four  times    the  required    bending 
moment;   as   we   have   seen,  this    does    not  affect    the    result. 
Since  the  depth  of   the  beam  is  fixed,  /,  and  r  cannot  be  as- 
sumed, but  must  be  found,  together  with  a. 

We  have 

d  —  2/i  +  2/2  =  12  —  2  =  10  inches,  and  y2  =  10  —  yr 
From  (6  a) 
MO  =  T%  x  12  X  500^'  +  f  X  12  X  500^(10  -  yt)  =  187,500, 


EXCESSIVE  REINFORCEMENT  397 

Solving,  we  have          yt  =  6  inches  nearly, 
and  ?/2  =  10  —  6  =  4  inches. 

From  (4)  **-  =  ^  ' 

?/i      fcE. 

Substituting  values  of  y^y^  fe,  Ec&nd  Et,  we  have 
/,  =  6,667  Ibs.  per  sq.  in. 

From(5)       .-!£*-  fxjjjjgx  6  -JOin. 

and  az  —  3.6  sq.  in.  of  metal  to  each  foot  width  of  beam.  This 
is  more  than  double  the  amount  of  reinforcement  required  for 
a  13.25  inch  beam,  while  the  steel  is  stressed  only  6,667  Ibs. 
per  square  inch. 

It  may  be  asked  why  not  use  a  smaller  area  of  metal,  say 
2  sq.  in.,  stressed  to  12,000  Ibs.  per  square  inch,  giving  the  same 
total  tension;  but  a  moment's  consideration  shows  that  in  order 
that  the  metal  should  assume  this  higher  stress,  its  elongation 
must  increase  proportionally,  involving  a  corresponding  in- 
crease of  strain  in  the  concrete  in  compression  with  an  accom- 
panying increase  in  stress  beyond  the  assumed  safe  limit  of 
500  Ibs.  per  sq.  in. 

591.  To  pursue  this  subject  of  excessive  reinforcement  a 
little  further,  let  us  examine  some  tests  of  concrete-steel  beams 
made  by  Prof.  Gaetano  Lanza  and  reported  in  Trans.  Am. 
Soc.  C.  E.  for  June,  1903. 

In  these  beams  the  width  z  =  8  inches,  h  =  12  and  d  =  10 
inches  nearly.  The  span  was  11  feet.  Proportions  in  concrete 
by  volume  1  part  Portland  cement,  3  parts  sand,  4  parts  broken 
trap  that  would  pass  1  inch  ring,  and  2  parts  of  the  same  rock 
that  would  pass  %  inch  ring.  Both  plain  and  twisted  square 
steel  bars  were  used  as  reinforcement,  the  plain  bars  having  a 
tensile  strength  of  about  sixty  thousand  pounds  per  square 
inch  and  the  twisted  steel  about  eighty  thousand  pounds  per 
square  inch. 

If  we  assume  the  ultimate  strength  of  the  concrete  to  be 
2,000  pounds  per  square  inch,  the  modulus  of  elasticity  at  this 
high  stress  to  be  1,400,000  and  the  modulus  of  the  steel  to  be 
28,000,000,  we  have, 

28,000,000 


R 


1,400,000 


398  CEMENT  AND  CONCRETE 

and  for  twisted  bars, 

80,000 

r  =  ^ooo-  =  40' 

'  From  Eq.  (4)        ?/2  =  ^y,  =  2 y1} 

•'•  37/j  =  10  inches,  y^  —  —inches. 

o 

From  E(i.  (5)a=  -^  =^X  ^-X  -^  =^  =  .055,  and  az  =.444. 
or       o       o       4U      lo 

That  is,  .444  sq.  in.  of  twisted  steel  reinforcement  is  required 
in  the  beam  8  inches  wide  in  order  that  the  stresses  in  concrete 
and  steel  shall  simultaneously  reach  the  values  of  2,000  and 
80,000  Ibs.  per  square  inch,  respectively. 

From  (6)  M  =  8  X  2000  X  g  +  f  X  ^ 

=  311,100  inch-pounds. 

One  beam  having  .56  sq.  in.  reinforcement,  or  an  area  very 
close  to  the  theoretical  amount  called  for  above,  broke  under  a 
bending  moment  of  470,000  inch-lbs.  Eight  other  beams  hav- 
ing a  greater  area  of  reinforcement  gave  moments  of  355,000 
to  443,000  inch-lbs.,  and  the  average  of  the  nine  bars  was  403,000, 
or  30  per  cent,  greater  than  the  value  derived  by  formula. 

592.  Included  in  the  series  of  .tests  were  three  beams,  in 
each  of  which  were  placed  two  1^  inch  twisted  rods.  As  we 
have  seen,  the  correct  amount  of  steel  to  develop  the  full  strength 
of  both  steel  and  concrete  is  about  .444  sq.  in.;  the  three  bars 
mentioned  had  3.12  sq.  inches  of  steel,  or  a  large  excess  of 
reinforcement.  To  determine  the  theoretical  moment  of  re- 
sistance of  these  beams,  assume  as  before: 

Es  =  28,000,000, 
Ec=  1,400,000, 
fe  =  2,000. 

From(4)  *=f;  t'^i 

1.25s  X  2 

a  =  -^—=.39. 


STRENGTH  OF  BEAMS  399 

2    2  000 

From  (5)  a  =  .39  =  -          -ylt  (6) 

d       /« 

2/2=10  —  2/1.  (c) 

Solving  (a),  (6)  and  (c),  we  obtain 
/.,  =  22,000,     ?/!  =  6.45  inches,     and     //2  =  3.55  inches; 

whence  r  =-'  =  11, 

7C 
and  from  ((>), 


\lt>  =  8  X  2000  f  -—  -f      X  — J(6.45)a  =  522,000  inch-pounds. 

These  three  beams  developed  the  following  moments  of  re- 
sistance: 553,550,  663,700  and  783,500,  mean  667,000  inch-lbs., 
or  28  per  cent,  greater  than  that  derived  by  formula.  None  of 
them  failed,  however,  by  crushing  of  the  concrete  at  the  top 
of  the  beam,  but  by  longitudinal  shearing  "at  or  a  little  above" 
the  reinforcing  rods. 

593.  It  appears,  then,  that  by  increasing  the  area  of  steel 
reinforcement  over  600  per  cent.,  or  from  .44  sq.  in.   to  3.12 
sq.  MIS.,  the  strength  of  the  beams  was  increased  about  68  per 
cent,  by  theory,  or  66  per  cent,  according  to  the  few  tests  cited. 
The  cost  of  the  beam,  however,  was  increased  about  one  hun- 
dred per  cent. 

This  method  of  increasing  the  moment  of  resistance  of  a 
beam  is  not  economical;  it  is  better  to  improve  the  quality  of 
the  concrete.  It  may,  however,  be  necessary  at  times  to  use 
excessive  reinforcement  on  account  of  restrictions  on  the  size 
of  beam,  but  one  may  easily  carry  this  so  far  that  he  passes 
outside  the  true  theory  of  concrete-steel  construction,  and  it 
becomes  a  question  of  the  steel  being  sufficient  to  carry  the 
entire  load.  In  such  cases  double  reinforcement  may  be  adopted. 

594.  Tables    of    Strength.  —  In    Table    160,    equations    (5) 
and  (6)  have  been  reduced  to  simpler  forms  by  the  introduc- 
tion of  values  of  Es  and  /.,.     Selecting  in  the  table  the  division 
corresponding   to    the    modulus   of    elasticity   of    the   concrete 
which  is  to  be  used,  and  the  line  opposite  the  assumed  stress  in 
the  concrete,  M0  =  quantity  in  column  a  times  the  square  of  the 
depth  of  beam,  d;  and  the  area  of  steel  in  a  beam  of  12  inch 
width,  i.e.  12  a,  equals  quantity  in  column  b  times  the  depth 


400 


CEMENT  AND  CONCRETE 


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SHIII 

STRENGTH  OF  BEAMS  401 

of  beam,  d.  Column  c  gives  the  area  of  cross-section  of  steel 
expressed  as  the  per  cent,  of  the  area  of  section  above  the  center 
of  steel  reinforcement. 

595.  For  example,  suppose  we  wish  to  know  the  strength  of 
a  beam  ten  inches  deep  (d  =  h  —  i  =  10  in.)  and  the  amount 
of  steel  required  to  develop  a  stress  in  the  concrete  of  400  Ibs.  per 
square  inch  when  the  stress  in  steel  is  10,000  Ibs.  per  sq.  in., 
and   the   modulus  of  elasticity  of  the  concrete  is  assumed  at 
3,000,000.     In  column  a  under  3,000,000  modulus,  and  opposite 
400  Ibs.  stress,  we  find  68.1 ;  then  the  moment  of  resistance  of  a 
beam  one  inch  wide  is  68.1  inch-lbs.  X  10  X  10  =  6,810  inch- 
Ibs.,  and  the  resistance  of  a  beam  12  inches  wide  is  6,810  foot- 
Ibs.     The  area  of  steel  required  in  12  inches  width  of  beam  is 
.092  d  or  0.92  sq.  in.     This  beam  is  reinforced  with  .77  of  one 
per  cent,  steel.     Similar  tables  may  be  prepared  for  other  values 
of  .7,  and  /,  if  desired. 

596.  In    Table     161    the    equations    have    been    completely 
solved    for   certain   typical   values  of  Ec  and  /0   assuming  the 
values  for  Es  and  /,  of  thirty  million  and  ten  thousand  respec- 
tively,  as  in  Table   160.     Having  computed  the  bending  mo- 
ment,  and   fixed   upon   the   probable   safe   working  stress   and 
modulus  of  elasticity  of  the  concrete  which  it  is  proposed  to 
use,  it  is  only  necessary  to  take  from  the   table  the  required 
depth  of  beam  and  the  amount  of  steel  reinforcement  required. 

For  example,  a  girder  10  feet  long  supported  at  the  ends 
carries  two  loads  of  5,000  pounds,  each  load  being  2.5  feet  from 
a  support. 

If  the  width  of  girder  is  15  inches,  working  stress  of  concrete 
300  Ibs.  per  sq.  in.  and  modulus  of  elasticity  of  concrete  1,500,000, 
what  is  the  required  depth  of  girder  and  area  of  steel  in  tension 
side? 

The  maximum  bending  moment  (neglecting  weight  of  beam) 
is  12,500  ft.-lbs.  throughout  the  central  five  feet.  The  required 

12 

moment  of  resistance  for  twelve  inches  in  width  is  —  of  12,500 

=  10,000  ft.-lbs.  Looking  in  the  table  for  this  bending  moment 
under  300  Ibs.  stress  and  1,500,000  modulus,  we  find  it  is  be- 
tween d  =  12  and  d  =  14,  or  at  about  d  =  13  inches.  If  we 
allow  2  inches  below  center  of  steel  reinforcement,  we  have 
total  depth  of  beam,  h  =  13  +  2  =  15  inches.  In  the  same 


402 


CEMENT  AND  CONCRETE 


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STRENGTH  OF  BEAMS  403 

lines  we  find  area  of  steel  for  12  inch  width  between  1.08  and 
1.26,  or,  say,  1.17;  then  for  15  in.  width  the  required  area  is  — 

X  1.17  =  1.46  sq.  in.     The  bars  should  not  be  more  than  3  to 

9 
6  inches  apart.     We  may  use,  then,  5  bars  —  inch   square   or 

-inch  diameter,  spaced  three  inches  apart.    In  large  beams  it  is 

o 

necessary  to  consider  the  bending  moment  occasioned  by  the 
weight  of  the  beam  after  making  a  first  approximation  to  the 
size  required. 

597.  The  above  tables  are  prepared  on  the  assumption  that 
the  stress  in  concrete  shall  be  equal  to  the  value  selected  when 
the  stress  in  the  steel  reinforcement  reaches  10,000  Ibs.  per  sq. 
in.     From    the    equations,    other    tables    may    be    prepared    if 
desired,  in  which  the  working  stress  in  steel  shall  be   12,500, 
16,000  or  any  other  assumed  value.     The  tables  are  not  suited 
to  the  computation  of  beams  in  which  excessive  reinforcement 
is  used. 

As  to  actual  tests  of  the  performance  of  concrete  and  steel  in 
combination,  the  possible  variations  in  material  are  so  diverse 
and  the  cost  of  experiments  so  great  that  the  results  thus  far 
obtained  appear  somewhat  fragmentary,  but  each  investigator 
has  selected  a  small  branch  of  the  subject  for  experiment. 
Among  the  more  valuable  tests  in  this  line  may  be  mentioned 
the  following  : 

Tests  at  Massachusetts  Institute   Technology,  Prof.   Gaetano 

Lanza,  Trans.  Amer.    Soc.  C.  E.,  vol.    50,  p.  486. 
Tests  at  Purdue  University,  Prof.  W.  K.  Hatt,  Jour.  Western 

Soc.  Engrs.,  June,  1904. 
Tests  at  Rose  Polytechnic  Institute,  Prof.  Malvard  A.  Howo, 

Jour.  Western  Soc.  Engrs.,  June,  1904. 
Tests  at  University  of  Illinois,  Prof.  A.  N.  Talbot,  Proc.  Amer. 

Soc.  for  Testing  Materials,  1904. 

Tests  at  University  of  Wisconsin,  Prof.  F.  E.  Turneaure,  Proc. 
Amer.  Soc.  for  Testing  Materials,  1904. 

ART.  70.     CONCRETE-STEEL  BEAMS  WITH  DOUBLE  REINFORCE- 
MENT 

598.  We  have  seen  that  when  the  depth  of.  a  beam  is  limited 
by  structural  considerations  we  may  increase  the  normal  load 


404 


CEMENT  AND  CONCRETE 


by  excessive  reinforcement,  but  that  this  method  results  in  low 
stresses  in  the  steel  and  is  not  usually  economical.  We  may 
now  consider  the  effect  of  placing  reinforcing  rods  in  the  com- 
pression side  of  the  beam  as  well  as  in  the  tension  side. 


FIG.  14.  FIG.  15.  FIG.  1C. 

CROSS-SECTION  CROSS-SECTION  STRAIN   DIAGRAM. 

(Single  Reinforcement.)  (Double  Reinforcement.) 

Let  Fig.  14  represent  the  cross-section  of  a  beam  reinforced 
on  the  tension  side  with  sufficient  steel,  area  a,  to  develop  the 
proper  working  stresses  in  the  materials,  and  let  the  position 
of  the  neutral  axis  be  N  N.  If  at  distance  x  from  the  neutral 
axis  we  add  an  area  of  steel  A'  in  the  compression  side,  the 
position  of  the  neutral  axis  would  be  changed  for  similar  load- 
ing; but  if  at  the  same  time  we  place  in  the  tension  side  an  ad- 

A        x 
ditional  area  of  steel  A  such  that  -p  =  —  >    the  position  of  the 

neutral  axis  will  be  unchanged.  Let  //  =  stress  in  steel  in 
compression;  then  since  the  steel  must  suffer  the  same  deforma- 
tion as  the  surrounding  concrete  p  =  — .  Multiplying  the  last 

/  S  •" 

two  equations,  we  have,  f8  A  =  /',  A',  that  is,  we  have  added 
equal  forces  to  the  two  sides  of  the  beam,  and  have  increased 
the  moment  of  resistance  by  f,  A  (x  +  ?/2)  inch-pounds. 

599.  To  illustrate  the  application  of  this  principle  we  may 
take  the  beam  considered  in  §  591,  in  which  z  =  8,  R  =  20; 

444  20 

r  =  40,  az  =  .444,  a  =  ^-  =  .055,  /.  =  80,000,  yt  =  y  inches, 

yl=  --  in.,  and  M  =  311,100  inch-pounds. 

o 

When  the  area  of  reinforcement  in  the  tension  side  of  this 
beam  was  increased  to  az  =  3.12  sq.  in.  or  a  =  .39,  the  theo- 
retical bending  moment  was  increased  to  522,000  inch-pounds 
(§  592).  What  will  be  the  result  of  a  similar  increase  in  steel 
distributed  between  the  two  sides  of  the  beam? 


DOUBLE  REINFORCEMENT  405 

Let  k  —  distance  from  top  of  beam  to  center  of  reinforce- 
ment on  compression  side  =  2  inches, 

10  4 

then  x  —  y^  —  2"  =  ^ —  2  =  -  inches, 

o  o 

±\.  JL>  ^i  J.  vJ  «     A  At 

—f  =  -=--*-  —  =  0.4  or  A  =  0.4  A'. 
A        2/2      &       «* 

A  +  A'  =  .39  -  .055  =  .335 

1.4  A'  =  .335      A'  =  .24  ,4 '2  =     1.92 

A  =  .095  4s   =      .76 

9 

whence  a    =  .055  az    =      .44 

A  +  a    =  .150        Total  steel,  3.12  sq.   inches. 

//  =  ^  =  .4 /.  =  32,000. 

2/2 

Added  moment  of  resistance  equals 

Az  (x  +  y2)  /.  =  .095  x  8  X    ^x  80,000  =  486,400  in.-lbs. 

o 

And  total  moment  of  resistance  eq  uals 

311,100  +  486,400  =  797,500  inch-pounds. 

None  of  the  bars  in  the  series  mentioned  in  §591  had  as  large 
an  area  of  reinforcement  as  1.92  sq.  in.  on  the  compression  side. 

It  is  noticed,  first,  that  the  double  reinforcement  gives  bet- 
ter results  than  such  excessive  reinforcement  on  the  tension 
side;  second,  that  the  stress  in  steel  on  the  compression  side  is 
less  per  square  inch  than  that  in  tension;  and  third,  that  in 
case  a  large  addition  of  steel  is  made,  this  results  in  a  greater 
area  of  steel  in  compression  than  the  total  area  of  steel  in  ten- 
sion. In  practice  the  area  of  steel  in  compression  is  usually 
made  equal  to,  or  less  than,  the  area  in  tension,  but  beams  with 
double  reinforcement  are  seldom  accurately  designed. 

ART.  71.     SHEAR  IN  CONCRETE-STEEL  BEAMS 

600.  There  are  several  methods  of  failure  of  concrete-steel 
beams  other  than  those  considered  above,  direct  tension  in  the 
steel  or  direct  compression  in  the  concrete  due  to  the  bending  mo- 
ment.   These  other  methods  of  failure  are  popularly  called  failures 
in  shear,  although  some  of  them  cannot  properly  be  so  classed. 

601.  We  have  seen  that  the  shearing  stress  of  concrete  is 
usually   considered   to   be  somewhat   in   excess   of  the   tensile 


406  CEMENT  AND  CONCRETE 

strength  (§458)  and  that  the  latter  is  one-fifth  to  one-tenth  the 
compressive  strength.  With  a  beam  having  only  a  normal 
amount  of  reinforcement,  then,  there  is  little  danger  to  be 
feared  from  simple  vertical  shear,  and  as  a  matter  of  fact,  tests 
have  not  developed  instances  of  such  weakness.  In  compara- 
tively short  spans,  however,  failures  have  occurred  near  the 
quarter  points,  in  cracks  starting  at  the  under  side  of  the  beam 
and  extending  upward  in  a  direction  inclined  toward  the  center. 
This  method  of  failure  has  the  appearance  of  being  due  to  a 
combination  of  shear  and  tension  in  the  lower  section  of  the 
beam,  since  the  cracks  are  approximately  at  right  angles  to  the 
theoretical  "  lines  of  direct  tension."  Such  failures,  however, 
are  almost  always  accompanied  by  a  slipping  of  the  steel  bar  in 
the  concrete,  and  may  frequently  be  prevented  by  taking 
proper  precautions  against  such  slipping. 

602.  A  more  frequent  cause  of  failure  is  a  longitudinal  shear 
in  the  plane  near  the  steel  reinforcement  and  on  that  side  of  it 
lying  nearer  the  concave  side  of  the  beam. 

It  is  evident  that  a  failure  caused  by  slipping  of  the  bar  in 
the  beam,  although  caused  primarily  by  shearing  forces,  is 
really  a  failure  in  adhesion,  yet  the  two  forms  of  weakness  are 
so  closely  connected  that  it  is  simpler  to  consider  them  together. 

603.  Comparison  with  Plate  Girder.  —  In  a  steel  plate  girder 
the  lower  flange  is  considered  to  carry  the  tension,  the  upper 
flange  the  compression;  the  web  connects  the  two  flanges,  caus- 
ing them  to  act  together  as  one  beam,  and  we  may  think  of 
the  web  as  preventing  the  ends  of  the  compression  flange  sliding 
beyond  the  ends  of  the  tension  flange.     When  the  web  is  not 
able  to   accomplish  this  without  buckling,   it  is  stiffened   by 
vertical  angles. 

In  a  concrete  steel  beam  we  have  considered  the  entire 
tension  to  be  carried  by  the  steel  reinforcement,  and  the  entire 
compression  to  be  carried  by  the  concrete  on  the  other  side  of 
the  neutral  axis.  The  connecting  web  is  also  concrete.  This 
web  is  thick  and  not  liable  to  buckle,  but  it  may  shear  in  a  lon- 
gitudinal plane  as  a  wooden  beam  may  do  when  short  and  deep. 
All  of  the  tension  in  the  steel  reinforcement  must  be  trans- 
mitted through  the  surrounding  concrete.  If  there  are  no  pro- 
jections on  the  steel  bar,  the  adhesion  of  the  concrete  to  it 
may,  under  certain  circumstances,  be  not  strong  enough  to 


SHEAR  IN  BEAMS  407 

safely  carry  this  stress;  and  if  the  adhesion  is  sufficient,  then 
the  shearing  strength  of  the  concrete  may  be  too  low  to  transmit 
the  stress  to  contiguous  fibers  or  layers. 

604.  Illustration.  —  Let  us  consider  a  concrete-steel  beam 
twelve  inches  wide,  twelve  inches  deep  and  of  ten  foot  span, 
supported  at  the  ends;  reinforcement,  one  square  inch  of  metal 
properly  distributed  in  a  plane  two  inches  above  the  bottom 
of  the  beam.  Let  us  suppose  this  beam  carries  a  uniform  load 
of  600  pounds  per  foot,  giving  a  maximum  bending  moment  of 
90,000  inch-lbs.,  and  a  stress  in  steel  of  10,000  pounds  at  the 
center.  The  ends  of  the  steel  bars  are  of  course  without  stress. 
Since  the  bending  moment  at  any  section  of  such  a  beam  is 
proportional  to  the  product  of  the  segments  into  which  the 
section  divides  the  span,  the  bending  moment  one  foot  from 
the  ends  will  be 

^  X  90,000  =  32,400  inch-pounds, 
o  X  o 

Let  us  consider  the  neutral  axis  in  the  same  position  at  the 
end  of  the  beams  as  near  the  center.  (This  is  not  strictly  true, 
because  of  the  lighter  stress  near  the  ends  of  the  beam,  but 
the  error  made  by  such  an  assumption  will  be  unimportant  for 
our  present  purpose.)  Then  the  tension  in  the  steel  will  have 
the  same  proportion,  or,  tension  in  steel  one  foot  from  the  end 
=  2\  X  10,000  =  3,600  pounds. 

The  stress  in  steel,  then,  which  is  zero  at  the  end,  has  in- 
creased to  3,600  Ibs.  in  one  foot  of  length.  To  provide  against 
poor  contact  near  the  end,  consider  two-thirds  of  this  length, 
or  eight  inches,  to  be  operative.  If  the  reinforcement  consists 
of  four  one-half-inch  square  bars,  the  necessary  adhesion  per 

S600 

square  inch   is  £  — -  =  57  Ibs.  per  sq.  in. ;  but  if  only  one  bar 
o  X  o 

is  used  one  inch  square,  the  required  adhesion  is  114  Ibs.  per 
sq.  in.  The  latter  would  not  be  good  practice,  not  only  be- 
cause of  high  adhesion  required,  but  because  the  steel  is  not 
properly  distributed. 

Where  the  stress  in  adhesion  is  greater  than  can  be  safely 
relied  upon  for  plain  rods,  it  is  necessary  to  use  some  kind  of 
deformed  bar,  or  to  anchor  the  bar  securely  at  the  end.  This 
may  be  done  by  passing  the  end  of  the  tension  bar  around  a 


408  CEMENT  AND  CONCRETE 

rod  transverse  to  the  beam  near  the  end.  Care  should  be  taken 
that  the  safe  value  of  adhesion  is  not  assumed  too  high. 

605.  Value  of  Shear.  —  The  same  total  stress  of    3,600  Ibs. 
must  be  transferred  through  the  concrete  immediately  above 
the  bar.     If  the  reinforcement  is  so  distributed  that  the  entire 
width   of  the  beam   has   practically   the   same  stress,   and   we 
consider,  as   before,  that  two-thirds  of  the   length  of  the  end 

3  600 

foot  is  operative,   we  have  mean  shear  =  ~—  —  =  37.5   Ibs. 

LZ   X   o 

per  sq.  in.  The  value  of  stress  in  shear  should  not  exceed  one- 
tenth  the  safe  value  in  compression,  and  there  is  a  general  ten- 
dency to  use  not  more  than  one-twentieth. 

If  the  same  form  of  beam  had  a  span  of  but  five  feet  with 
same  bending  moment,  the  value  of  the  shearing  stress  by  this 
method  becomes  75  Ibs.  per  sq.  in.,  and  it  will  be  necessary  to 
provide  against  this  stress  coming  upon  the  concrete. 

Another  approximate  method  is  the  ordinary  one  for  rect- 
angular beams,  viz.  to  consider  the  shear  in  horizontal  plane 
just  above  the  steel  reinforcement  to  be  f  times  the  total  shear 
at  any  section,  divided  by  the  area  of  vertical  section  of  the 
beam. 

606.  Provision  is  sometimes  made  for  relieving  the  concrete 
of  all  shearing  stresses.     In  this  case  the  beam  is  divided  into 
imaginary   panels   of  length   equal,   say,   to   the   depth   of   the 
beam,    and   the   diagram   of   maximum   shear   is   drawn.     The 
shear  in  each  imaginary  panel  is  then  provided  for  by  a  vertical 
or  inclined  bar  of  the  proper  dimensions.     Or,  what  is  usually 
better,  the  shear  bars  are  all  of  one  size  and  the  proper  num- 
ber of  them  are  distributed  throughout  each  panel  length;  the 
spacing  of  the  shear  bars  thus  becomes  wider  near  the  center 
of  the  beam. 

607.  Resistance   to  Shear.  —  When  provision   against   shear 
is  made  by  using  small  steel  rods  placed  either  vertical  or  in- 
clined downward  toward  the  center  of  the  beam,  as  mentioned 
above,    these  rods  may  well  be  made  in  the  form  of  inverted 
U-shaped   stirrups,   with   their   ends   securely   fastened   to   the 
reinforcing  metal  in  tension. 

In  many  cases  all  the  provision  necessary  is  given  by  the  use 
of  two  longitudinal  bars,  parallel  and  close  together  near  the  cen- 
ter of  the  span,  but  one  of  them  leading  to  a  plane  near  the  top  of 


SHEAR  IN  BEAMS  409 

the  beam  at  the  supports.  This  system  is  very  conveniently 
applied  in  concrete  slabs  supported  by  I-beams,  one  bar  of  the 
pair  being  hooked  over  the  upper  flanges  of  the  I-beam  and 
sagging  toward  the  center.  The  Hennebique  system  (§571)  is 
a  combination  of  the  inclined  bar  and  U-shaped  stirrups. 

608.  A  modification  of  the  single  inclined  bar  is  the  Cum- 
mings  system,  wherein  there  are  several  pairs  of  bars  of  vary- 
ing lengths;  these  are  all  horizontal  and  near  the  bottom  along 
the  center  of  the  beam;  a  short  distance  from  the  center  the 
shortest  pair  turns  up  at  an  angle  of  about  forty-five  degrees;  a 
littVe  farther  toward  the  end  a  second  pair  of  bars  is  turned  up, 
and  so  on,  leaving  a  single  pair  to  go  through  straight  to  the 
support. 

Another,  arid  more  radical  modification,  is  the  Kahn  system 
(§573),  in  which  the  bar  is  square  with  wings  of  metal  on  oppo- 
site corners  which  are  sheared  and  bent  up  at  angles  of  forty- 
five  degrees,  so  that  the  outline  of  the  steel  work  in  a  beam 
resembles  the  tension  members  of  a  Pratt  truss. 


CHAPTER    XX 

SPECIAL  USES  OF  CONCRETE:  BUILDINGS,  WALKS, 
FLOORS  AND   PAVEMENTS 

ART.  72.     BUILDINGS 

609.  While  the  use  of  concrete  and  steel  for  the  walls  and 
floors  of  buildings  is  about  fifty  years  old,  yet  it  is  only  in  com- 
paratively  recent  years   that  its  value   has  become   generally 
known.     It  is  now  applied  to  all  classes  of  structures,   ware- 
houses, factories,  residences,  station  and  office  buildings,   and 
it  is  anticipated  that  in  the  next  twenty  years  concrete-steel 
will  be  as  familiar  in  architecture  as  steel  skeleton,  stone,  and 
brick  are  now. 

610.  It  happens  that  at  present  the  concrete-steel   building 
industry  is  largely  in  the  hands  of  companies  who  are  exploiting 
some  particular  form  of  steel  rods  or  bars  applied  according  to 
some  one  of  the  many  " systems"  of  reinforcement.     This  con- 
dition has  both  good  and  bad  features.     A  reputable  concern  of 
this  kind  will  have  in  their  employ  engineers  who  should  sat- 
isfy themselves  that  each  design  is  a  safe  one,  for  the  failure 
of  a  building  will  cast  disrepute  on  their  particular  system.     It 
is  this  fact  that  leads  the  companies  to  keep  the  construction 
entirely,  and  the  design  largely,  in  their  own  hands.     Another 
advantage  is  that  these  concerns  are  able  to  perfect  methods  of 
construction  by  experience,  and  to  lessen  the  expense  of  one 
structure  by  making  use  of  the  concrete  plant  and  the  molds 
that  have  been  used  on  another. 

611.  In   making  plans   for  a  building,  the  owner  is  usually 
represented  in  the  first  instance  by  an  architect  whose  business 
it  is  to  dictate  the  design.     If  concrete-steel  is  considered,  the 
architect  may  call  an  engineer  in  consultation  and  they  may 
together  harmonize  the  features  of  utility  and  appearance  with 
economy  and  strength,  but  in  letting  the  contract  it  is  found 
that  the  competition  is  limited  to  one  or  two  companies  using 
the  particular  system   which   the   engineer   considers  the  best 
adapted  to  the  particular  conditions  in  question. 

410 


BUILDINGS  411 

On  the  other  hand,  the  architect  will  hesitate  to  go  to  the  con- 
struction company  for  assistance,  since  he  must  first  select  the 
system  he  shall  use,  a  question  upon  which  his  ideas  may  be  neither 
clear  nor  well  grounded,  and  he  is  then  having  the  prospective 
contractor  assist  in  the  design.  Under  these  circumstances  the 
architect  will  usually  consider  concrete-steel  construction  as 
something  he  wishes  to  avoid  if  possible.  But  this  condition 
will  correct  itself  in  time,  for  owners  will  demand  a  considera- 
tion of  this  form  of  construction,  engineers  will  become  fa- 
miliar with  its  use  and  will  be  employed  to  design  the  engineer- 
ing features,  while  reliable  contractors  in  every  city  will  obtain 
permission  to  build  in  accordance  with  any  " system"  under 
the  supervision  of  a  competent  engineer. 

612.  Roof.  —  While  a  pitch  roof   is  sometimes  built  of  con- 
crete-steel, this  form  of  construction  is  particularly  adapted  to 
so  called  flat  roofs.     The  roof  is  constructed  much  the  same  as 
a  floor  slab  (Art.  65-67),  except  that  expansion  joints  are  some- 
times provided,  and  the  roof  is  covered  with  tar  and  gravel, 
or  some   of   the   patent   roofings   ordinarily   used.     While   the 
roof  loads  are  usually  light,  permitting  a  greater  span  of  slab 
between  beams  than  for  floor  construction,  it  will  seldom  be 
economical    to    introduce    these   longer   spans    because   of   the 
changes  necessary  in  the  molds.     In  most  buildings  it  is  neces- 
sary to  provide  against  condensation,  and  for  this  purpose  a 
flat  ceiling  may  be  suspended  at  the  level  of  the  under  side  of 
the  beams  giving  an  air  space. 

613.  Floor  System.  —  The  floors  may  be  constructed  in  con- 
formity with    the  principles    stated    in    Chapter    XIX.      The 
strength    of    short   span   arches,    such   as    are  used  for  floors, 
where  the  haunches  are  built  up  level  with  the  top  of  crown 
of  arch,  is  a  matter  of  experiment  and  cannot  be  accurately 
determined  theoretically.     Empirical  formulas  may  be  derived 
for  a  certain  system   based  on  a  sufficient  number  of  tests. 
The  principles  underlying  the  strength  of  slabs  may  be  con- 
sidered the  same  as  those  applying  to  beams  (Art.  69),  although 
if  the  length  of  slabs  is  not  much  greater  than  the  span,  they 
are  not  strictly  applicable,  but  will  err  on  the  safe  side. 

614.  A  decision  must  first  be  made  as  to  the  size  of  bays  into 
which  the  floor  space  is  to  be  divided.     This  will  of  course  de- 
pend on  the  use  of  the   building,  the  engineering  features  con- 


412  CEMENT  AND  CONCRETE 

forming  to  requirements  of  utility.  If  the  bays  are  not  square, 
the  girders  should  usually  take  the  shorter  span  between  columns. 
This  length  is  then  divided  into  the  number  of  slab  spans  that 
will  give  maximum  economy.  The  shorter  these  spans  the  less 
the  amount  of  material  required  in  slabs  and  the  greater  the 
number  and  cost  of  floor  beams.  Computations  should .  be 
made,  therefore,  for  two  or  three  arrangements  to  determine 
this  point.  As  this  distribution  for  maximum  economy  will 
vary  with  the  loads  to  be  provided  for,  it  is  well,  if  the  floors 
are  not  all  to  carry  the  same  load,  to  take  for  this  computation  a 
load  intermediate  between  the  heaviest  and  lightest,  and  use  if 
possible  the  same  arrangement  of  spans  throughout  the  building. 
The  strength  of  slabs  for  given  bending  moments  may  be 
taken  directly  from  Table  161,  after  deciding  upon  the  working 
stress  to  be  allowed  in  the  concrete  and  the  probable  modulus 
of  elasticity.  The  beams  and  girders,  if  single  reinforcement 
is  used,  are  taken  from  the  same  table  or  computed  by  the 
methods  of  Art.  69. 

615.  In  some  instances  it  may  be  found  economical   to  use 
concrete-steel  slabs  for  floors  supported  by  concrete  protected 
steel  beams  and  girders.     One  advantage  of  this  system  is  that 
the   forms   for  building   the   protecting   concrete   and   for   the 
floor  slabs  may  be  hung  from  the  steel  girders  and  beams.     For 
this   method   of   construction   the   enveloping   concrete   should 
not  be  less  than  one  and  one-half  inches  thick  over  the  edges  of 
flanges,   and   wire  fabric   or   metal  lath   wrapped   about   lower 
flanges  of  beams  will  insure  the  concrete  remaining  in  place. 
This   is   not   properly   concrete-steel   construction,   but   simply 
concrete  protected  steel,  and  except  in  case  the  concrete  ex- 
tends well  above  the  steel,  forming  an  independent  compres- 
sion flange,  no  added  strength  should  be  computed  for  the  con- 
crete covering. 

616.  Columns.  —  In  the  foundations  of  buildings  of  moder- 
ate  height  the  supporting   columns   may  be   built  entirely  of 
concrete.     Since,  however,  the  pressure  on  the  concrete,  even 
when  it  is  constructed  with  the  greatest  care,  should  not  ex- 
ceed two  hundred  to  three  hundred  pounds  per  square  inch, 
the  required  area  of  cross-section  in  the  lower  stories  is  usually 
so  great  as  to  preclude  the  use  of  columns  built  entirely  of 
concrete. 


BUILDINGS  413 

617.  Concrete   Filling   and   Covering.  —  A   steel    column   of 
any  of  the   ordinary  styles,   built  up  of  steel  shapes   may  be 
used,  and  protected  from  corrosion  and  fire  by  filling  and  cover- 
ing with  concrete.     This  not  only  serves.  as  a  protection  against 
rust,  but  materially  increases  the   stiffness  and  permits  the  use 
of  a  somewhat  higher  working  stress  in  the  steel.     The  concrete 
filling  should  be  mixed  quite  wet  in  order  that  it  shall  work 
into  all  angles.     The  edges  of  the  metal  should  not  approach 
nearer  than  one  and  one-half  inches  to  the  exterior  of  the  con- 
crete, and  flat  surfaces  of  metal  should  have  a  covering  of  at 
least  two  and  one-half  inches.     Where  it  is  necessary  to  cover 
large,  flat  surfaces,  they  should  be  first  covered  with  expanded 
metal  or  wire  fabric,  locked  on  by  twisting  around  the  edges 
of  the  plate  or  channel. 

618.  COLUMNS  OF  CONCRETE  STEEL.  —  Concrete-steel  col  - 
umns  differ  from  the  above  in  that  the  main  dependence  is 
placed   on  the   concrete  rather  than  on  the  steel.     For  such 
columns  longitudinal  reinforcement  has  generally  been  employed. 
Steel  bars  extending  from  end  to  end  of  the  column  are  dis- 
tributed throughout  the  cross-section,  and  are  tied  together  at 
intervals  of  four  to  twelve  inches  by  smaller  bars  forming  loops 
to  hold  them  in  place.     The  splicing  of  the  bars  is  effected  by 
placing  a  small  tube  over  the  upper  end  of  the  lower  bar  and 
projecting  above  it,  and  then  setting  the  lower  end  of  the  upper 
bar  within  the  tube  resting  on  the  lower  bar.     Where  this  is 
done  it  is  essential  that  the  two  ends  be  planed  perfectly  square, 
and  it  is   much  better  to  avoid  splices  in  a  column  between 
lateral  supports.     In  a  building  the  reinforcing  rods  project  up 
through  the  floor  above  and  are  spliced  into  the  bars  of  the 
columns  in  the  next  story. 

619.  Strength  of  Columns.  —  When  a  column  reinforced  with 
longitudinal  bars   is  subjected   to   pressure,   the   concrete  and 
steel  must  shorten  together.     The  relative  stresses  in  the  two 
materials  will  then  be  proportional  to  their  moduli  of  elasticity. 
From  this  follows  the  formula, 


P  =  /c  (C 

where  P  =  total  pressure  on  column, 

fc  =  stress  in  concrete, 
C  and  S  =  areas  of  concrete  and  steel  respectively, 


414  CEMENT  AND  CONCRETE 

W 

and  R  =  ^,  or  ratio  of  the  modulus  of  elasticity 

•&C 

of  the  steel  to  that  of  the  concrete. 

In  a  series  of  tests  of  twenty-one  columns  made  by  Prof. 
Gaetano  Lanza,1  but  three  failed  under  a  lower  stress  than  that 
computed  by  the  above  formula.  The  columns  were  eight  to 
ten  inches  square,  six  to  seventeen  feet  long  and  reinforced 
with  either  one  or  four  bars,  the  latter  being  from  f  inch  to  1J 
inches  square. 

The  lowest  breaking  load  was  fifty  tons  on  an  8  by  8  inch 
column  with  one  bar  one  inch  square,  and  the  strongest  column, 
10  by  10  inches,-  with  four  J  inch  longitudinal  bars,  was  not 
crushed  with  a  load  of  one  hundred  fifty  tons,  the  limit  of  the 
testing  machine.  The  lowest  result  was  twenty  per  cent,  less 
than  that  given  by  the  formula,  and  the  greatest  excess  strength 
over  the  theoretical  was  fifty  per  cent. 

620.  While  longitudinal  reinforcement  undoubtedly  strength- 
ens a  long  column  against  flexure,  as  well  as  adds  to  the  resist- 
ance to  crushing,  yet  the  added  strength  is  gained  at  the  ex- 
pense of  considerable  additional  cost.     Suppose  we  have  a  ten 
inch  square  column,  twelve  feet  long,  made  of  concrete  with  a 
breaking  load   of   1,800  Ibs.    per  square  inch,   or   180,000  Ibs. 
total  breaking  load.     Suppose  eight  }  inch  square  bars  to  be 
built  into  this  column  as  longitudinal  reinforcement,  and  that 
the  modulus  of  elasticity  of  the  steel  is  ten  times  that  of  the 
concrete.     Then  the  strength  of  the  reinforced  column  would 
be,  by  the  formula  above, 

P  =  1,800  (95.5  +  (10  X  4.5))  =  252,900. 

The  longitudinal  reinforcement  has  thus  resulted  in  an  increase 
of  strength  of  40  per  cent.,  while  by  the  addition  of  180 
pounds  of  metal,  the  cost  of  the  column  has  risen  from  about 
$3.00  to  say  $8.50,  an  increase  of  about  180  per  cent,  without 
counting  the  cost  of  lateral  ties,  and  the  additional  trouble  in 
building  a  reinforced  column. 

621.  Hooped  Concrete.  —  In  extended  experiments  on  what 
he  has  called  "  hooped  concrete,"  M.  Considere2  has  shown  that 


1  Trans.  A.  S.  C.  E.,  Vol.  1,  p.  487. 

2  Comptes  Rendus  de  I' Academic  des  Sciences,   1898-1902.     Translation, 
"Reinforced  Concrete,"  by  Armand  Considere,  translated  by  Leon  S.  Mois- 
seiff,  McGraw  Publishing  Co.,  New  York, 


BUILDINGS  415 

reinforcement  is  much  more  important  and  beneficial  in  a 
transverse  or  circumferential  direction  than  if  longitudinal. 
This  may  be  accounted  for  by  the  fact  that  the  natural  method 
of  failure  of  concrete  prisms,  is  by  splitting  along  planes  parallel 
to  the  direction  of  pressure,  and  the  ordinary  method  of  failure 
by  shear  along  inclined  surfaces  is  induced  by  the  friction  of 
the  plates  transmitting  the  pressure  to  the  prism.  It  was  also 
shown  that  while  concrete  reinforced  by  longitudinal  bars  with 
the  ordinary  amount  of  lateral  ties  breaks  suddenly,  hooped 
concrete  fails  gradually  under  a  much  heavier  load. 

622.  M.  Considere  concluded  from  his  experiments  that  the 
circumferential   ties    should    not    be   farther    apart    than    one- 
seventh  to  one-tenth  the  diameter  of  the  column,  even  when 
longitudinals  were  used  to  assist  in  completing  the  network, 
and  that  the  results  were  more  successful  the  nearer  together 
the  hoops  or  ties   were  placed.     He  found   that  spirals   were 
better  than  individual  single  ties  and  that  longitudinals  were  of 
value  chiefly  in  assisting  to  confine  the  concrete,  transmitting 
the  bursting  pressure  at  a  given  plane  to  the  contiguous  spirals 
above  and  below. 

623.  M.  Considere  says1  that  the  "  Compressive  resistance  of 
a  hooped  member  exceeds  the  sum  of  the  following  three  ele- 
ments :  — 

"1.  Compressive  resistance  of  the  concrete  without  rein- 
forcing. 

"2.  Compressive  resistance  of  the  longitudinal  rods  stressed 
to  their  elastic  limit. 

"3.  Compressive  resistance  which  could  have  been  produced 
by  imaginary  longitudinals  at  the  elastic  limit  of  the  hooping 
metal,  the  volume  of  the  imaginary  longitudinals  being  taken 
as  2.4  times  that  of  the  hooping." 

To  subject  hooped  concrete  to  a  practical  test,  M.  Considere 
constructed,  in  1903,  a  truss  bridge  of  sixty-five  foot  span  with 
parabolic  top  chord  of  seven  and  one-half  feet  rise,2  the  com- 
pression members  being  of  hooped  concrete,  and  the  tension 
members  of  concrete-steel  with  longitudinal  reinforcement,  or 
concrete  protected  steel.  A  central  panel  of  the  truss  was  con- 


" Reinforced  Concrete,"  p.  159. 
2  Engineering  News,  May  5,  1904. 


416  CEMENT  AND  CONCRETE 

structed  with  a  reduced  section  of  top  chord  about  eight  inches 
diameter  reinforced  by  eight  longitudinal  bars  .43  inch  in 
diameter  and  a  helix  6J  inches  in  diameter  of  .43  inch  metal 
coiled  to  a  pitch  of  about  one  inch.  This  reduced  top  chord 
section  showed  signs  of  failure  when  the  computed  stress  reached 
about  5,000  pounds  per  square  inch. 

624.  FORMS  FOR  BUILDINGS.  —One  of  the  most  serious  prob- 
lems in  the  construction  of  concrete-steel  buildings  is  the  de- 
signing of  the  forms.  They  must  be  as  light  as  is  consistent 
with  strength  to  facilitate  handling.  They  should  be  of  simple 
construction  so  that  they  may  be  set  up  and  removed  without 
too  much  supervision,  and  they  should  be  so  assembled  with 
bolts  and  screws  that  they  may  be  used  repeatedly.  In  erect- 
ing a  large  building  sufficient  forms  are  usually  provided  to  set 
up  one  floor  complete,  including  columns,  beams,  girders  and 
floor  slabs.  After  placing  the  reinforcement,  the  concrete  is 
filled  in  as  rapidly  as  possible,  making  the  slabs,  girders  and 
columns  practically  monolithic. 

The  forms  for  the  girders  usually  rest  upon  the  column 
molds  and  are  supported  at  intermediate  points  by  posts  rest- 
ing on  the  completed  floor  below.  While  column  molds  are 
sometimes  filled  from  the  top,  better  work  is  assured  by  having 
one  side  of  the  mold  built  up  as  the  concrete  is  filled  in  from 
the  side. 

The  mold  to  receive  the  concrete  forming  the  floor  slab  is 
either  a  part  of,  or  is  supported  by,  the  pieces  forming  the 
sides  of  the  girders  and  beams.  Provision  is  sometimes  made 
for  leaving  supports  at  intervals  under  the  completed  beams 
and  girders  after  removing  the  forms  from  the  sides  of  the  beams 
and  the  bottom  of  floor  slabs.  This  is  done  by  making  the 
bottom  piece  of  the  girder  mold  separate,  and  attaching  the 
side  pieces  to  it  by  screws  which  may  be  removed  without  dis- 
turbing the  bottom.  The  caps  of  the  supporting  posts  are  then 
made  long  enough  to  permit  the  lower  edges  of  the  side  pieces 
to  rest  directly  on  them.  This  method  was  adopted  in  build- 
ing the  Central  Felt  and  Paper  Company's  factory  at  Long 
Island  City.1 


1  Wight-Easton-Townsend  Company,  Contractors,    Engineering  Record, 
Jan.  16,  1904. 


BUILDINGS 

625.  In  the  same   building  the  walls  were  built  with  molds 
three  feet  high  and  sixteen  feet  long,  placed  in  pairs  on  oppo- 
site sides  of  the  wall.     When  one  section  was  completed,  the 
molds  were  "lifted  until  the  lower  edges  were  two  inches  below 
the  top  of  the  concrete.     In  the  new  position  they  were  sup- 
ported by  horizontal  bolts  through  their  lower  edges,  across  the 
top   of  the   concrete;  the   upper  edges   were   tied  together  by 
transverse  wooden  strips  nailed  to  them  about  three  feet  apart, 
and   they   were  braced  to  the  false  work  supporting  the  roof 
and  column  molds."     "The  bolts  passed  through  sleeves  which 
were  left  permanently  embedded  in  the  walls.     At  first,   iron 
pipes  were  used  for  this  purpose,   but  afterwards  it  was  dis- 
covered that  pasteboard  tubes  were  equally  efficient  and  much 
easier  to  trim  and  point  after  the  molds  were  removed." 

626.  An    excellent  system  of  molds  was  used  in  the  con" 
struction  of  the  Kelley  and  Jones  Company's  factory  at  Greens- 
burg,  Pa.1     The  floor  molds  were  especially  convenient,  being 
made  collapsible  by  a  hinge  joint  at  the  top  along  the  longi- 
tudinal  center  line.     These   floor   molds   were  in   reality   cores 
between  adjacent  floor  beams;  when  in  place  the  top  surface 
was  horizontal,  to  form  the  under  side  of  the  floor  slab,  and 
the  vertical  side  pieces   formed  the  sides  of  the  floor  beams. 
When  the  concrete  had  set  sufficiently,  the  lower  edges  of  the 
form  were  made  to  approach  each  other,  thus  coming  away 
from  the  concrete  gradually.    A  special  light  wooden  framework 
or  tower,  with  a  working  platform  six  feet  below  the  floor,  and 
a  rope  sling  to  receive  and  lower  the  floor  mold,  permitted  of 
removing  the  molds  rapidly  and  without  injury.    A  special  truck 
was  also  used  for  moving  the  floor  molds  about  the  building. 

627.  A  convenient  adjunct  for  the  construction  of  concrete 
wall  forms  consists  of  a  short  section  of  I-beam  having  a  width 
between  flanges  equal  to  the  thickness  of  the  plank  to  be   used. 
These  plank  holders  are  laid  in  pairs,  with  web   horizontal,  one 
on  either   side    of   the   wall,  and   connected  by  a  bolt  passing 
through  them  and  through  the  wall.2     Two  rows  of  planks  on 
edge  are  first  placed  around  the  building  so  as  to  inclose  the  pro- 


1  Mr.  E.  L.  Ransome,  Architect  and  Engineer,  Engineering  Record,  Feb. 
6  and  13,  1904. 

1  Patented  by  Thomas  G.  Farrell,  Washington,  N.  J. 


418  CEMENT  AND  CONCRETE 

posed  wall.  At  the  upper  side  of  each  junction  between  two 
planks  in  the  same  horizontal  row  is  placed  one  of  these  plank 
holders.  Another  horizontal  row  of  planks  may  now  be  placed, 
with  the  iron  plank  holders  at  the  joints  as  before.  As  the 
wall  is  built  up,  the  lower  planks  and  holders  may  be  removed 
and  placed  on  top,  and  thus  few  forms  are  required.  Tees  and 
L-forms  are  provided  for  partition  walls  and  corners. 

When  an  air  space  is  desired  in  a  wall  a  special  terra  cotta 
tile  or  building  block  may  be  built  into  the  wall,  but  this  is 
quite  expensive,  and  an  interior  collapsible  form  may  be  made 
of  timber  by  the  use  of  two  planks  held  apart  by  a  wooden 
brace  which  may  be  knocked  out.  Special  means  of  handling 
the  interior  plank  should  be  provided,  and  the  building  of  a 
high  wall  cannot  be  continuous  with  this  method. 

628.  New  York  Building  Regulations.  —  While  city  building 
regulations  are  not  always  criteria  of  good  practice,  yet  the 
Regulations   of   the   Bureau   of   Buildings   of   the    Borough   of 
Manhattan  concerning  the  use  of  concrete-steel  construction  are 
exceptional.     Emanating    from   a   bureau   that   has    been   dis- 
tinctly hostile  to  concrete-steel,  they  are  naturally  conservative, 
but  are,  on  the  whole,  excellent,  and  work  conscientiously  done 
in  accordance  with  them  will  not  bring  discredit  on  concrete 
construction. 

It  is  specified  that  the  cement  shall  be  only  high  grade 
Portland  standing  certain  tests,  that  the  sand  shall  be  clean 
and  sharp,  aggregate,  broken  trap,  or  gravel  of  a  size  that  will 
pass  a  three-quarter  inch  ring,  and  that  the  proportions  used 
shall  be  one  cement,  two  sand  and  four  of  stone  or  gravel,  or 
that  the  concrete  shall  have  a  crushing  strength  of  two  thou- 
sand pounds  per  square  inch  in  twenty-eight  days.  Only  the 
best  quality  of  concrete  is  thus  permitted. 

629.  The  Regulations  concerning  the  design  are  then  stated 
as  follows :  — 

"  Concrete-steel  shall  be  so  designed  that  the  stresses  in  the 
concrete  and  the  steel  shall  not  exceed  the  following  limits:  — 

Extreme  fiber  stress  on  concrete  in  compression,       500  Ibs.  per  sq.  in. 

Shearing  stress  in  concrete 50       "  " 

Concrete  in  direct  compression 350       "  " 

Tensile  stress  in  steel 16,000      "  " 

Shearing  stress  in  steel 10,000      "  " 


BUILDINGS  419 

"The  adhesion  of  concrete  to  steel  shall  be  assumed  to  be 
not  greater  than  the  shearing  strength  of  the  concrete. 

"The  ratio  of  the  moduli  of  elasticity  of  concrete  and  steel 
shall  be  taken  as  one  to  twelve. 

"The  following  assumption  shall  guide  in  the  determination 
of  the  bending-moments  due  to  the  external  forces:  Beams  and 
girders  shall  be  considered  as  simply  supported  at  the  ends,  no 
allowance  being  made  for  the  continuous  construction  over 
supports.  Floor  plates  when  constructed  continuous  and  when 
provided  with  reinforcement  at  top  of  plate  over  the  supports, 
may  be  treated  as  continuous  beams,  the  bending-moment  for 

W  L 

uniformly  distributed  loads  being  taken  at  not   less  than  — -  ; 

W  L 

the  bending-moment  may  be  taken  as  -— -  in  the  case  of  square 

floor  plates  which  are  reinforced  in  both  directions  and  sup- 
ported on  all  sides.  The  floor  plate  to  the  extent  of  not  more 
than  ten  times  the  width  of  any  beam  or  girder  may  be  taken 
as  part  of  that  beam  or  girder  in  computing  its  moment  of 
resistance. 

"The  moment  of  resistance  of  any  concrete-steel  construc- 
tion under  transverse  loads  shall  be  determined  by  formulas 
based  on  the  following  assumptions:  - 

"(a)  The  bond  between  the  concrete  and  steel  is  sufficient 
to  make  the  two  materials  act  together  as  a  homogeneous  solid. 

"(6)  The  strain  in  any  fiber  is  directly  proportionate  to  the 
distance  of  that  fiber  from  the  neutral  axis. 

"(c)  The  modulus  of  elasticity  of  the  concrete  remains  con- 
stant within  the  limits  of  the  working  stresses  fixed  in  these 
Regulations. 

"From  these  assumptions  it  follows  that  the  stress  in  any 
fiber  is  directly  proportionate  to  the  distance  of  that  fiber  from 
the  neutral  axis. 

"The  tensile  strength  of  the  concrete  shall  not  be  considered. 

"When  the  shearing  stresses  developed  in  any  part  of  a 
construction  exceed  the  safe  working  strength  of  concrete,  as 
fixed  in  these  Regulations,  a  sufficient  amount  of  steel  shall  be 
introduced  in  such  a  position  that  the  deficiency  in  the  resist- 
ance to  shear  is  overcome. 

"When  the  safe  limit  of  adhesion  between  the  concrete  and 


420  CEMENT  AND  CONCRETE 

steel  is  exceeded,  some  provision  must  be  made  for  transmitting 
the  strength  of  the  steel  to  the  concrete. 

"  Concrete-steel  may  be  used  for  columns  in  which  the  ratio 
of  length  to  least  side  or  diameter  does  not  exceed  twelve. 
The  reinforcing  rods  must  be  tied  together  at  intervals  of  not 
more  than  the  least  side  or  diameter  of  the  column. 

"The  contractor  must  be  prepared  to  make  load  tests  on 
any  portion  of  a  concrete-steel  construction,  within  a  reasonable 
time  after  erection,  as  often  as  may  be  required  by  the  Super- 
intendent of  Buildings.  The  tests  must  show  that  the  con- 
struction will  sustain  a  load  of  three  times  that  for  which  it  is 
designed,  without  any  sign  of  failure." 

ART.   73.     CONCRETE  WALKS 

630.  One  of  the  most  important  uses  of  concrete  is  in  the 
construction  of  street  and  park  walks.     It  has  not  only  driven 
stone  nagging  almost  out  of  use,  but  it  is  being  employed  to  a 
large  extent  in  towns  and  villages  where  board   walks  have 
formerly  been  used  almost  exclusively. 

A  concrete  walk  is  made  up  of  a  sub-base  or  foundation,  a 
base,  and  a  wearing  surface. 

631.  Foundation.  —  As  in  other  structures,  one  of  the  most 
important  essentials  for  success  lies  in  the  preparation  of  the 
foundation,   and  the   care  that  must  be  bestowed  on  it  will 
depend  upon  the  character  of  the  soil  and  the  climate.     In  the 
higher  latitudes  of  the  United  States,  frost  may  soon  destroy  a 
walk  the  foundation  of  which  is  not  well  drained. 

The  excavation  should  be  made  to  the  sub-grade  previously 
determined  upon,  any  objectionable  material  such  as  loam  or 
organic  matter  being  removed,  and  the  bottom  of  the  excava- 
tion smoothed  and  well  rammed.  Upon  this  is  laid  the  sub- 
base,  its  thickness  varying  from  nothing  to  twelve  inches.  In 
a  sandy  soil  with  good  natural  drainage  and  little  danger  from 
frost,  and  where  light  traffic  is  expected,  it  may  be  unnecessary 
to  provide  any  special  sub-base,  since  the  soil  itself  furnishes  a 
good  foundation  for  the  concrete,  but  in  clay  soil  in  northern 
climates,  twelve  inches  of  sub-base  may  be  required.  The  best 
material  for  this  sub-base  is  broken  stone  varying  in  size  from 
one-half  inch  to  two  and  one-half  inches.  Usually  broken 
stone  is  considered  too  expensive,  and  gravel,  coarse  sand, 


CONCRETE  WALKS  421 

cinders,  or  broken  brick  is  employed.  A  layer  four  inches  thick  is 
usually  sufficient  for  good  materials,  but  six  to  twelve  inches  of 
cinders  are  sometimes  required.  It  should  be  well  rammed  to 
a  level  surface,  and  when  completed  should  be  firm  but  porous. 
The  most  important  point  is  that  this  course  shall  have 
good  drainage,  otherwise  it  may  be  a  menace  to  the  walk.  If 
it  is  more  porous  than  the  retaining  soil,  it  will  naturally  drain 
this  soil,  and  if  the  water  is  not  able  to  escape  into  the  sewer 
or  elsewhere,  it  may  be  frozen  and  heave  the  walk.  An  ex- 
cellent plan  sometimes  adopted  is  to  lay  at  intervals  of  twenty 
to  twenty-five  feet,  a  blind  stone  drain  from  the  walk  founda- 
tion to  the  foundation  of  the  curb.  In  exceptional  cases  it  may 
be  necessary  to  lay  a  tile  drain  in  the  sub-base  to  lead  the  water 
away  from  the  walk. 

632.  Base.  —  The  base  is  the  body  of  the  walk  giving  stiff- 
ness to  the  structure.  Its  functions  are  to  furnish  a  solid 
foundation  for  the  wearing  surface  and  to  give  transverse 
strength  to  the  walk,  transmitting  the  pressure  uniformly  to 
the  sub-base.  The  base  is  of  concrete,  which  need  not  be  very 
rich  for  ordinary  traffic.  A  proportion  of  one  part  packed 
Portland  cement  to  two  and  one-half  volumes  of  dry  sand 
and  six  volumes  broken  stone  is  excellent,  and  proportions  of 
one,  three  and  seven  parts  cement,  sand  and  stone,  respectively, 
will  usually  be  found  sufficient,  though  the  richer  the  concrete  in 
the  base  the  better  will  the  top  dressing  adhere  to  it. 

The  broken  stone  for  this  concrete  should  be  of  a  size  not 
exceeding  one  and  one-half  inches  in  any  dimension,  some  cities 
requiring  three-quarters  inch  or  less.  Crushed  granite  and  trap 
are  excellent,  though  limestone  or  any  other  moderately  hard 
rock  may  be  used  that  is  suited  to  making  concrete  for  ordinary 
purposes.  If  of  a  hard  rock,  the  screenings  may  well  be  left 
in  the  broken  stone,  and  when  this  is  done,  the  dose  of  sand 
should  be  diminished.  (See  Art.  37.) 

The  thickness  of  the  layer  of  concrete  should  not  be  less 
than  three  inches.  Four  inches  is  much  better  and  is  recom- 
mended for  general  use  in  sidewalks,  while  in  exceptional  cases 
six  inches  is  required.  The  top  of  the  concrete  base  should 
be  finished  to  a  plane  parallel  to  the  proposed  surface  of  the 
walk  and  at  a  distance  below  it  equal  to  the  proposed  thickness 
of  the  top  dressing. 


422  CEMENT  AND  CONCRETE 

633.  Wearing  Surface.  —  The  preparation  and  application 
of  the  wearing  surface  require  much  care  if  satisfactory  results 
are  to  be  obtained.  The  most  evident  service  of  this  layer  is 
to  withstand  wear,  and  it  should  therefore  be  made  of  rich 
Portland  cement  mortar.  With  a  sand  consisting  principally 
of  quartz  particles,  it  is  found  that  a  mortar  composed  of  equal 
parts  cement  and  sand  gives  about  the  best  results  in  tests  of 
abrasion.  If  the  mortar  is  used  richer  than  this,  it  is  likely  to 
check  or  crackle  in  setting,  marring  the  appearance  of  the  walk. 
Mortar  containing  two  parts  cement  to  three  parts  sand  gives 
nearly  as  good  results,  and  two  parts  sand  or  fine  crushed 
granite  to  one  of  Portland  cement  is  usually  satisfactory.  The 
sand  for  the  mortar  should  be  quartz  if  possible,  or  crushed 
granite  or  trap.  It  should  be  screened  through  a  quarter 
inch  mesh,  and  there  should  not  be  a  large  proportion  of 
very  fine  particles. 

The  thickness  of  the  layer  of  top  dressing  is  usually  about 
one  inch,  and  this  is  probably  the  maximum  thickness  ever 
required.  One-half  inch  of  top  dressing  is  believed  to  be  suf- 
ficient when  the  wear  is  not  excessive,  provided  the  base  has 
been  carefully  leveled. 

634.  The  Construction  of  the  Walk.  —  If  the  walk  has  not  a 
considerable  longitudinal  slope,  it  should  be  given  a  transverse 
slope  of  about  a  quarter  inch  to  the  foot  to  provide  for  draining 
the  surface. 

Stakes  for  grade  and  line  having  been  given,  a  maitre  cord 
is  stretched  along  the  line  stakes  to  mark  the  sides  of  the  exca- 
vation. After  the  material  has  been  excavated  to  the  proper 
sub-grade  and  all  soft  material  in  the  bottom  removed,  the 
bottom  of  the  trench  is  well  rammed.  If  tile  drain  is  necessary, 
it  is  laid  with  open  joints  on  this  foundation.  The  material  to 
form  the  sub-base  is  now  wheeled  in  and  rammed  to  the  proper 
thickness,  water  being  used  freely  if  it  facilitates  the  packing. 
The  top  of  the  sub-base  is  brought  to  a  level  plane  at  the  proper 
distance  below  the  grade  stakes. 

The  molds  for  the  walk  are  now  to  be  laid.  These  are  made 
of  two  by  four  or  two  by  six  inch  scantling,  sized  and  dressed 
on  at  least  one  side  and  one  edge.  Stakes  are  first  securely 
driven,  about  five  or  six  feet  apart,  with  their  faces  two  inches 
back  from  the  side  lines  of  the  proposed  walk,  and  their  tops 


f ' 

CONCRETE  WALKS  423 

at  grade.  Against  these  stakes  the  scantlings  are  placed  on 
edge  with  dressed  side  toward  the  walk,  and  smooth  edge  level 
with  the  grade  stakes.  These  molds  are  held  in  place  by  nail- 
ing through  the  supporting  stakes  into  the  scantling,  and  if 
these  nails  are  not  driven  "home,"  they* may  easily  be  pulled 
to  release  the  mold  when  the  work  is  completed.  On  the  upper 
edges  of  the  mold  are  then  marked  off  the  sizes  of  blocks  de- 
sired, being  careful  that  the  marks  defining  a  joint  are  exactly 
opposite  each  other  on  the  two  scantlings. 

635.  The  concrete  materials  having  been  previously  deliv- 
ered near  the  work,  the  concrete  is  mixed,  either  by  hand  or 
machine,  according  to  the  methods  already  given,  and  rammed 
in  place  after  the  sub-base  has  been  well  wet  down  to  receive 
the  concrete.     The  concrete  should  be  just  short  of  quaking, 
and  in  ramming  care  must  be  taken  not  to  disturb  the  molds. 
For  tamping  next  the  molds,  the  makers  of  cement  working 
tools  offer  a  light  rammer  with  square  face  at  one  end  and 
blunt,  chisel  shaped  tamper  at  the  other.     The  surface  of  the 
base  is  brought  to  a  plane  parallel  to  the  proposed  finished  sur- 
face of  the  walk,  and  at  a  distance  below  it  equal  to  the  thick- 
ness of  the  top  dressing.     A  straight  edge,  long  enough  to  span 
the  walk  and  notched  out  at  the  ends  so  that  when  placed  on 
the  molds  the  straight  edge  will  define  the  correct  grade  of  the 
base,  is  a  convenience  here. 

636.  The   concrete  is   now   cut  into    blocks   exactly   corre- 
sponding to  the  proposed  blocks  in  the  top  dressing.     For  this 
purpose  a  straight  edge  is  laid  across  the  walk  in  line  with 
marks  previously  made  on  the  molds  to  define  the  joints,  and 
with  a  spade  or  special  tool  the  concrete  base  is  cut  entirely 
through  to  the  sub-base.     This  division  is  necessary  to  allow  for 
expansion  and  contraction,  and  prevent  cracks  in  the  top  dressing 
elsewhere  than  at  the  joints.      This  joint  in  the  base  should 
then  be  filled  with  clean  sand.     If  preferred,  these  joints  in  the 
base  may  be  made  by  placing  thin  steel  strips  across  the  molds 
to  be  removed  after  the  concrete  for  the  next  block  is  in  place. 

The  end  block  made  from  a  given  batch  of  concrete  should 
be  limited  by  a  cross  mold  set  exactly  on  line  of  a  proposed 
joint.  When  the  base  is  continued,  this  cross  mold  is  removed. 
A  part  of  a  block  should  never  be  molded  and  then  built  on 
after  having  stood  long  enough  to  begin  to  set.  Any  concrete 


424  CEMENT  AND  CONCRETE 

left  over  from  finishing  a  block  should  either  be  mixed  in  with 
the  next  batch,  if  this  is  to  follow  in  a  very  short  time,  or  it 
should  be  wasted.  A  disregard  of  this  rule  will  probably  result 
in  a  crack  in  the  top  dressing  above  the  line  of  division  between 
adjacent  batches. 

637.  When  a  block  of  base  is  finished,  the  top  dressing  or 
wearing  surface  should  be  applied  immediately.     The  lack  of 
adhesion  between  the  base  and  wearing  surface  is  one  of  the 
most  frequent  causes  of  failure  in  cement  walks.     The  mortar 
should  not  merely  be  laid  on  in  a  thick  layer  and  then  struck 
off  to  grade,  but  it  should  be  worked  and  beaten  into  close  con- 
tact with  the  concrete  at  every  point.     The  mortar  should  be 
tamped  with  a  light  rammer  and  beaten  with  a  wooden  batten, 
and  to  accomplish  this  properly  the  mortar  must  not  be  very 
wet.     The  surface  is  then  to  be  struck  off  with  a  straight  edge 
bearing  on  the  top  of  the  mold  planks.     Some  hollows  or  rough 
places  will  remain,  and  the  straight  edge  should  be  run  over  a 
second  or  perhaps  a  third  time,  a  small  amount  of  rather  moist 
mortar,  made  from  thoroughly  screened  sand,  having  been  first 
applied  to  such  places. 

When  the  surface  film  of  water  is  being  absorbed,  the  surface 
is  worked  with  a  wooden  float.  The  exact  time  when  the  work 
should  be  floated  will  soon  be  known  by  experience.  After  the 
floating  is  completed,  the  trowel  may  be  used  to  give  a  smoother 
surface,  but  this  makes  the  walk  so  slippery  that  it  is  not  usually 
desirable. 

638.  If  the  top  dressing  is  worked  too  long,  the  cement  is 
brought  to  the  surface,  robbing  the  next  lower  layer  of  its  ce- 
ment and  resulting  in  scaling.     The  top  dressing  is  now  cut 
entirely  through  on  exact  line  above  the  joints  in  the  base. 
This  may  be  done  by  a  trowel  working  against  a  straight  edge, 
but  special  tools  are  made  for  cutting  through  the  mortar  and 
rounding  the  edges  of  the  joint  at  one  operation.     A  quarter- 
round  tool  is  also  run  along  the  edges  of  the  mold  to  give  a  neat 
finish.     When   desired,    an   imprint   roller   run   over   the   walk 
gives  it  the  appearance  of  having  been  bushhammered. 

It  is  important  that  the  top  dressing  be  applied  before  the 
concrete  has  begun  to  set,  and  it  must  not  be  applied  to  a  por- 
tion of  a  block  and  then  some  time  allowed  to  elapse  before 
applying  the  remainder.  The  edge  of  the  top  dressing  must 


CONCRETE  WALKS  425 

be  cut  off  squarely  at  the  end  of  the  block.  If  desired,  the 
wearing  surface  may  be  colored  by  the  use  of  lamp  black  in  the 
mortar,  giving  a  uniform  gray  color  to  the  walk.  (§  535.) 

639.  When  the  walk   is  completed,  it  should  be  fenced  off 
so  that  animals  may  not  walk  over  it  while  still  fresh,  and  it 
should  be  protected  from  a  hot  sun.     The  surface  should  be 
kept  moist,  and  this  may  be  done  after  the  first  twenty-four 
hours  by  spreading  a  layer  of  damp  sand  over  the  walk  and 
wetting  the  sand  with  a  rose  nozzle  as  often  as  may  be  needed. 
The  walk  may  be  opened  to  light  travel  after  about  four  days,  but 
it  is  better  to  remain  covered  with  the  damp  sand  for  a  week. 

640.  Cost  of  Concrete  Walk.  —  The  cost  of   concrete  walks 
varies  from  ten  cents  to  twenty-five  cents  per  square  foot.     A 
fair  price  for  a  walk  of  average  quality  where  there  are  no 
special  difficulties  is  twelve  to  eighteen  cents  per  square  foot. 

As  an  instance  of  a  walk  built  with  special  care,  the  one 
constructed  about  the  top  of  the  bank  of  the  Forbes  Hill  Reser- 
voir may  be  mentioned.1  The  sub-base  of  this  walk  was  of 
stone  and  twelve  inches  thick,  the  layer  of  concrete  was  five 
inches  thick  at  the  center  of  the  walk  and  four  inches  at  the 
sides.  The  top  was  of  granolithic  finish  one  inch  in  thickness. 
The  walk  was  laid  in  separate  blocks  about  six  feet  square. 
The  average  gang  employed  on  the  concrete  consisted  of  six 
men  and  one  team,  while  the  finishing  was  done  by  two  masons 
and  one  tender.  The  amount  laid  per  day  was  about  forty 
square  yards.  The  cost  per  square  yard  was  as  follows:  - 

$  cu.  yd.  stone  in  foundation  or  sub-base,  at  $.40  per  cu.  yd.  .    $0.133 
Labor,  placing  stone  at  $1.50  per  day     .........    .        .502 

Total  cost  stone  foundation  per  sq.  yd.  of  walk     .    .    .  $0.035 

.158  bbl.  cement,  at  $1.53  per  bbl.       ...    ........    $0.242 

.065  cu.  yd.  sand,  at  $1.02  per  cu.  yd  ............  060 

.109  cu.  yd.  stone,  at  $1.57  per  cu.  yd  ............  170 

Labor,  mixing  and  placing  concrete     ............  450 

Total  cost  concrete  base  per  sq.  yd  .........  "    $0.028 

.11  bbl.  cement,  at  $1.53  per  bbl  .............    $0.168 

.022  cu.  yd.  sand,  at  $1.02  per  cu.  yd  ............  022 

Lamp  black      ......................  008 

Labor,  preparing  and  finishing  surface    ...........  140 

Total  cost  top  dressing  or  wearing  surface      .....    "  $0.347 


Total  -t  walk  per  sq.  yd.  |  J^  »;?$    ;   ;    ;   ; 


C.  M.  Saville,  M.  Am.  Soc.  C.  E.,  Engineering  News,  March  13,  1902. 


426  CEMENT  AND  CONCRETE 

641.  The  following  is  given  as  an  estimate  of  cost  of   items 
in  a  walk  built  with  six  inch  cinder  sub-base,  four  inch  concrete 
base  and  one  inch  top  dressing . 

COST    PER    SQ.    YD.    OP    WALK 

MATERIALS          LABOR 

Preparation  of  foundation,  excavation  and  ramming   .    .    .  $0.20 

Sub-base,  6  in.  cinders  £  cu.  yd.,  at  $0.40  cu.  yd $0.07 

Placing  and  ramming  cinders 0.04 

^  cu.  yd.  concrete,  at  $3.00  per  cu.  yd.  for  materials  alone    .  0.33 

|  cu.  yd.  concrete,  placing,  at  $1.80  per  cu.  yd 0.20 

Top  dressing  ¥V  cu.  yd.  mortar,  at  $9.00  per  cu.  yd.    .    .    .  0.25 

Placing  top  dressing  and  finishing  walk 0.25 

Superintendence  and  molds 0.10 

Totals $0.65  $0.79 

Total  cost  per  sq.  yd.,  $1.44,  or  16  cents  per  sq.  ft. 

642.  As  an  example  of  a  low  priced  walk,  the  concrete  walks 
in  San  Francisco  1  are  but  three  inches  thick,  two  and  one-half 
inches  of  concrete  composed  of  one  part  Portland  cement,  two 
parts  beach  gravel,  and  six  parts  of  crushed  rock  of  size  not 
exceeding  one  inch;  the  top  dressing  being  one-half  inch  thick 
of  equal  parts  Portland  cement  and  beach  gravel.     With  ce- 
ment $2.50  per  bbl.,   crushed  rock  and  gravel  from  $1.40   to 
$1.75  per  cu.  yd.,  and  wages  twenty  cents  an  hour  for  laborers 
and  forty  cents  for  finishers,  this  walk  is  constructed  at  from 
nine  to  ten  cents  per  square  foot.     It  is  stated  that  a  gang  of 
three  or  four  men  will  lay  150  to  175  square  feet  per  day. 

ART.  74.     FLOORS  OF  BASEMENTS,  STABLES  AND  FACTORIES 

643.  The  principles  governing  the  laying  of  walks  apply  also 
in  a  general  way  to  the  construction  of  floors  that  rest  directly 
on  the  ground. 

For  residences,  basement  floors  may  be  laid  with  three  inch 
base  of  concrete  and  one-half  inch  wearing  surface.  The  thick- 
ness of  sub-base  will  depend  upon  the  character  of  the  soil. 
Where  natural  conditions  do  not  assure  good  drainage  of  the 
foundation,  this  should  always  be  provided  for  by  either  a  blind 
stone  or  tile  drain  laid  around  the  outer  edge  of  the  building 
and  leading  to  the  sewer  or  other  outlet.  The  finished  surface 
of  the  floor  should  always  have  a  slight  slope  toward  the  center 


Engineering  News,  March  4,  1897. 


FLOORS  427 

or  one  corner  of  the  basement,  and  a  trapped  sewer  connection 
set  at  this  lowest  point  in  such  a  way  that  it  is  accessible  for 
repairs  and  cleaning. 

644.  Wet  Basements.  —  Where   much  ground   water  is   en- 
countered, and  especially  where  a  basement  is  subjected  to  a 
head  of  water  from  without,  special  precautions  must  be  taken 
in  building  the  floor.     The  concrete  must  be  made  thick  enough 
so  that  its  weight  and  the  arch  action  set  up,  shall  be  able  to 
withstand  the  upward  pressure  of  the  water.     In  building  such 
a  floor  it  is  necessary  to  keep  a  sump  hole,  preferably  in  the 
center,  towards  which  the  construction  proceeds  from  the  sides. 
A  pipe  placed  in  the  sump  hole  permits  pumping  until  the  con- 
crete is  laid  about  the  pipe,  when  the  latter  may  be  filled  with 
rich  cement  mortar.     In  such  cases  the  side  walls  of  the  base- 
ment should  be  plastered  with  Portland  cement  mortar  on  the 
outside  and  special  care  taken  in  joining  the  floor  to  the  wall. 

645.  Size  of  Blocks.  —  As  the  changes  in  temperature  in  a 
building  are  usually  much  less  than  in  open  air,  the  blocks  of 
concrete  may  be  of  much  larger  size,  say  ten  feet  square,  and 
many    basement   floors    are    laid    without    any   joints,    though 
sooner  or  later  they  will  probably  crack  if  so  laid.     In  factories 
for  certain  purposes,  however,  the  floors  may  be  subjected  to 
greater  changes  in  temperature   than  walks  laid  in  the  open 
air.     In  such  cases  the  blocks  should  not  be  more  than  three 
or  four  feet  on  a  side,  and  the  joints  may  well  be  filled  with 
asphalt,  especially  if  water-tightness  is  desired. 

646.  Stable  floors  may  be  made  of  six  inch  cobble  or  broken 
stone  sub-base,  six  inches  of  concrete  made  with  mortar  con- 
taining three  parts  sand  to  one  cement,  and  one  inch  of  top 
dressing  containing  three  parts  sand  (mixed  sizes)  or  crushed 
granite  to  two  parts  cement. 

Factories  having  heavy  machinery  with  much  vibration  re- 
quire strong  floors.  Such  a  floor  may  be  made  of  six  inches 
of  cobble  stone  sub-base  covered  by  six  inches  of  a  lean  concrete 
made  with  one-to-four  mortar,  and  above  this,  three  to  five 
inches  of  rich  concrete  made  with  mortar  containing  two  and 
one-half  parts  sand  to  one  cement,  and  one  inch  of  top  dressing, 
equal  parts  cement  and  sand  or  cement  and  crushed  granite. 

647.  Example  and  Cost.  —  In  the  construction  of  the  new 
printing  building  for  the  Government  Printing  Office  at  Wash- 


428  CEMENT  AND  CONCRETE 

ington,  the   basement  floor  is  nine  inches  thick,  made  as  fol- 
lows: * — 

1.  Concrete  sub-base,  six  inches  thick  of   one  part  natural 
cement,   two  parts  sand  and  four  and  one-half  parts  broken 
brick. 

2.  Concrete  base,  two  and  one-half  inches  thick  of  Portland 
cement  one  part,  sand  two  parts  and  fine  broken  gneiss  four 
parts. 

3.  Top   dressing,   one-half  inch  in   thickness,   of  two   parts 
sand  to  one  part  Portland  cement. 

The  cost  of  this  floor  was  about  $1.50  per  square  yard,  or 
about  seventeen  cents  per  square  foot. 

ART.  75.     CONCRETE  IN  PAVEMENTS  AND  DRIVEWAYS 

648.  PAVEMENT  FOUNDATIONS.  —  The  principal  use  of  con- 
crete in  connection  with  city  pavements  has  been  as  a  founda- 
tion, the  wearing  surface  being  of  some  other  material,  as  brick, 
asphalt,  cedar  blocks,  etc. 

Concrete  for  pavement  foundations  should  not  be  less  than 
six  inches  in  thickness,  and  a  greater  thickness  will  be  required 
where  the  ground  is  insecure.  The  excavation  having  been 
made  to  the  required  sub-grade,  and  all  loose  soil  removed  and 
the  places  refilled  with  broken  stone,  the  earth  is  thoroughly 
rolled  to  a  smooth  surface  parallel  to  the  surface  of  the  proposed 
pavement.  Drainage  for  the  foundation  should  be  provided 
where  necessary  by  broken  stone  or  tile  drains  beneath  the 
curb.  Before  beginning  the  placing  of  concrete,  stakes  may  be 
driven  in  the  foundation,  with  their  tops  at  grade,  at  intervals 
of  five  to  ten  feet  over  the  entire  pavement,  to  assist  in  securing 
the  proper  grade  of  concrete  surface. 

649.  The  stone  for  the  concrete  should  be  broken  so  that  no 
piece  is  larger  than  two  and  one-half  inches  in  its  greatest  di- 
mension.    If  the  stone  is  of  good  quality,  it  need  not  be  screened 
except  to  remove  the  finest  dust,  if  this  is  present  in  consider- 
able quantities.     Sufficient  mortar  should  be  used  to  fill  the 
voids  in  the  stone,  this  mortar  being  composed  of  about  two 
parts  sand  to  one  of  natural  cement,  or  better,  two  and  one- 
half  or  three  parts  sand  to  one  of  Portland  cement.     This  con- 


Report  of  Capt.  John  S.  Sewall,  Report  Chief  of  Engineers,  1896. 


PAVEMENTS  429 

crete  is  thoroughly  rammed  in  place,  care  being  taken  that 
adjacent  batches  as  laid  in  the  street  mingle  with  each  other 
so  as  to  show  no  line  of  demarcation.  In  stopping  work  for 
the  night,  the  concrete  should  cut  off  sharply  on  a  straight 
line  parallel  to  the  direction  of  the  proposed  joints  in  the  wear- 
ing surface.  Joints  extending  across  the  street  should  be  left 
at  intervals  of  thirty  to  forty  feet  to  allow  for  expansion  and 
contraction. 

650.  The  concrete  is  finished  to  a  surface  parallel  with  the 
proposed  street  surface,   a  templet  being  employed  to  secure 
this.     The  concrete  should  be  kept  damp  for  a  few  days,  and 
no  traffic  allowed  upon  it  until  the  wearing  surface  is  laid.     If 
the  wearing  surface  is  of  brick  or  wooden  blocks,  a  layer  of 
sand  about  one  inch  thick  is  first  spread  over  the  concrete. 

The  advantages  of  a  concrete  foundation  for  street  pave- 
ments are  its  strength  and  durability  and  water-tightness. 

651.  CONCRETE  PAVEMENT.  —  Concrete  has  not  been  a  popu- 
lar material  for  a  street  surface  except  for  short  driveways  arid 
in  courts  where  both  vehicles  and  pedestrians  must  be  accom- 
modated.    One  reason  for  this  is  that  concrete  is  slippery,  and 
another,  that  owing  probably  to  carelessness  or  ignorance,  the 
wearing  qualities  have  not  been  good.     The  first  objection  may 
be  largely  removed  by  cutting  the  surface  into  blocks,  four  by 
eight  inches,  by  deep  grooves,  or  by  the  use  of  a  deep  imprint 
roller  on  the  wearing  surface.     As  to  wearing  qualities,  there 
seems  to  be  no  good  reason   why  a  concrete  cannot  be  made 
tough  enough  to  withstand  heavy  traffic.     It  will  of  course  be 
necessary  to  divide  the  work  into  blocks  of  twenty  to  twenty- 
five   square   feet,    with   expansion   joints   of   sand,    asphalt,   or 
tarred  paper  between.     A  third  objection  is  the  glare  of  the 
surface  in  summer.     A  partial  remedy  for  this  may  be  had  by 
placing  some  coloring  matter,  such  as  lamp  black,  in  the  top 
dressing. 

652.  The  sub-base  may  consist  of  a  six  inch  layer  of  broken 
stone,  or  twelve  inches  of  cinders,  well  drained  and  thoroughly 
compacted  by  rolling.     For  exceptionally  heavy  wear  it  may  be 
advisable  to  use  a  five  inch  layer  of  lean  concrete  for  the  sub- 
base,  after  rolling  the  bottom  of  the  excavation  and  providing 
drainage. 

Upon  the  sub-base  should  be  laid  a  base,  composed  of  four 


430  CEMENT  AND  CONCRETE 

inches  of  concrete  made  with  first  class  stone,  such  as  granite, 
trap  or  hard  limestone  crushed  to  pass  a  ring  one  and  one-half 
inches  in  diameter,  and  containing  enough  mortar,  one  part 
Portland  cement  to  two  or  three  parts  sand,  to  fill  the  voids  in 
the  stone.  The  top  dressing,  a  layer  of  granolithic  one  and  one- 
half  or  two  inches  thick,  should  then  be  immediately  applied. 
This  mortar  should  be  made  with  one  or  two  parts  granite,  trap, 
or  other  hard  rock  crushed  to  pass  a  five-eighths  inch  screen,  to 
one  part  Portland  cement. 

These  two  layers  are  placed  in  much  the  same  manner  as 
that  described  for  laying  concrete  sidewalks,  but  the  joints  in 
base  and  top  dressing  should  run  at  angles  of  forty-five  degrees 
with  the  curb  to  prevent  ruts  following  the  lines  of  the  joints. 
A  roller  making  deep  imprints  is  then  run  over  the  finished 
surface  to  furnish  a  foothold  for  horses,  or,  for  this  purpose  a 
special  roller  may  be  used  to  mark  the  top  dressing  into  blocks 
approximately  four  by  eight  inches,  with  deep  (one-half  inch) 
grooves. 

When  completed,  the  pavement  should  be  kept  moist,  pref- 
erably by  a  layer  of  damp  sand,  and  no  traffic  should  be  al- 
lowed upon  it  for  at  least  a  week  or  ten  days. 

653.  Concrete  pavement  laid  in  Bellefontaine,  Ohio,  was 
found  to  be  in  good  condition  after  ten  years'  service;1  the 
only  serious  defect  apparent  being  that,  since  the  blocks  were 
marked  off  parallel  to  the  curb,  ruts  have  sometimes  formed 
along  these  joints.  This  pavement  was  made  with  four  inches 
base  concrete,  laid  directly  on  sub-grade  where  foundation 
is  gravel,  sand  or  porous  soil;  or  if  soil  is  impervious,  the 
base  was  laid  on  four  inches  of  broken  stone  or  cinders.  The 
top  layer  was  two  inches  thick,  equal  parts  cement  and  sand  or 
pea  granite.  Sub-drains  of  three  inch  tile  were  laid  inside  each 
curb  line,  and  the  curb  is  formed  as  part  of  the  outer  blocks. 
Both  the  base  and  top  dressing  were  cut  through  in  squares, 
five  feet  on  a  side.  The  cost  of  the  pavement  is  said  to  have 
been  $2.15  per  square  yard,  and  very  few  repairs  have  been 
found  necessary. 

In  Germany  a  cement  macadam,  made  with  six  inch  sub- 


1  Municipal  Engineering,  December,  1900,  and  Engineering  News,  Jan.  7, 
1904. 


CURBS  AND  GUTTERS  431 

base  of  broken  stone  or  gravel,  with  a  wearing  surface  of  hard 
macadam  stone  mixed  with  cement,  has  been  successfully  used. 

ART.  76.     CURBS  AND  GUTTERS 

654.  The  use  of   concrete  for  curbs  and  gutters  is  rapidly 
increasing.     Curbing  is  sometimes  molded  and  afterward  put  in 
place  like  stone  curbing,  but  the  greatest  advantages  in  the  use 
of  concrete  for  this  purpose  are  only  attained  by  molding  in 
place  the  curb  and  gutter  as  one  structure. 

The  Parkhurst  combined  curb  and  gutter  is  a  patented  form 
that  has  proved  very  satisfactory.  This  form  has  a  projection 
of  about  one  inch  at  the  back  and  another  along  the  bottom 
just  below  the  curb,  this  feature  being  patented. 

A  combined  curb  and  gutter  may  consist  of  a  curb  four  to 
six  inches  wide  at  the  top,  and  five  to  seven  inches  at  the  bot- 
tom, and  have  a  face  of  six  to  seven  inches  above  the  gutter. 
The  upper  face  corner  of  the  curb  and  the  angle  between  curb 
and  gutter  should  be  rounded  with  a  radius  of  one  and  one- 
half  to  two  inches.  The  gutter  is  sixteen  to  twenty  inches 
wide,  and  from  six  to  nine  inches  thick,  with  top  surface  con- 
forming to  the  grade  of  the  street. 

655.  The  sub-base  should  consist  of  a  layer  of  broken  stone 
six  inches  thick,  or  six  to  twelve  inches  of  cinders  thoroughly 
rammed.     The  preparation  of  the  foundation  should  be  similar 
to  that  required  for  a  pavement,   care  being  taken  that  the 
sub-base  be  thoroughly  drained,   tile  being  used  if  necessary. 
Forms  to  receive  the  concrete  are  held  in  place  by  stakes,  the 
molds  being  carefully  set  to  grade.     The  sub-base  may  now  be 
covered  by  a  layer  of  four  to  six  inches  of  Portland  concrete  of 
only  moderate  richness,  as  one  to  three  to  six,  and  the  concrete 
to  form  the  curb  and  gutter  placed  upon  it  before  it  has  set, 
or  a  six  inch  layer  to  form  the  gutter  may  be  placed  directly 
on  the  sub-base. 

656.  Concrete  to  form  the  curb  and  gutter  should  be  of  good 
quality,  not  more  than  two  and  one-half  parts  sand  to  one  part 
Portland  cement  being  used  for  the  mortar,  and  sufficient  mor- 
tar used  to  entirely  fill  the  voids  in  the  stone.     The  broken 
stone  for  this  concrete  should  be  rather  fine,  with  few,  if  any, 
pieces   larger  than  one  inch  in  greatest  dimension.     The  ex- 
posed faces  receive  a  top-dressing,  or  wearing  surface,  of  one- 


432  CEMENT  AND  CONCRETE 

half  inch  to  one  inch  of  granolithic  containing  not  more  than 
one  and  one-half  parts  of  trap  or  granite,  pea  size,  to  one  part 
Portland  cement.  This  coating  is  applied  as  soon  as  possible 
after  the  concrete  is  placed,  as  in  sidewalk  work.  The  surface 
is  troweled  or  floated,  but  a  smooth,  glossy  finish  is  avoided. 

The  curb  and  gutter  may  well  be  laid  in  alternate  blocks 
about  six  feet  long,  but  a  somewhat  neater  appearance  is  se- 
cured by  making  the  work  continuous,  and  cutting  it  entirely 
through  at  intervals  of  six  feet  to  provide  for  slight  movement. 
As  the  molds  may  be  used  repeatedly,  they  should  be  sub- 
stantially made.  Special  forms  are  of  course  required  at  corners, 
catch  basins,  etc.  As  in  other  concrete  construction,  the  work 
should  be  protected  from  injury  and  kept  moist  for  at  least  a 
week. 

657.  On  business  streets  it  is  desirable  to  build  the  sidewalk 
close  to  the  curb,  with  only  a  joint  between,  the  grade  of  the 
walk  conforming  to  the  curb  and  sloping  up  toward  the  build- 
ing line  one-quarter  inch  to  the  foot.  On  residence  streets  the 
walk  should  be  separated  from  the  curb  by  a  park  strip,  the 
walk  being  high  enough  to  give  drainage  toward  the  curb. 

Steel  facing  is  sometimes  used  for  curbs  subjected  to  excep- 
tional wear,  as  in  front  of  shipping  warehouses  and  freight 
sheds.  Where  these  are  applied,  they  should  cover  the  top 
and  the  upper  part  of  the  face  of  the  curb  and  must  be  well 
anchored,  by  bolts  or  special  webs,  to  a  substantial  mass  of 
concrete,  otherwise  they  will  work  loose  and  defeat  the  object 
for  which  they  are  used. 

658.  Cost  of  Concrete  Curb  and  Gutter.  —  At  Champaign, 
111.,1  a  curb  was  built  seven  inches  high  and  five  inches  thick, 
the  gutter,  six  inches  thick,  extending  nineteen  inches  into  the 
roadway  from  the  face  of  the  curb.  The  foundation  consisted 
of  six  inches  of  gravel  or  cinders  well  rammed.  The  concrete 
was  composed  of  one  part  Portland  cement  to  five  parts  fine 
gravel,  and  the  finishing  coat,  one  inch  thick,  was  of  one  part 
Portland  cement  to  one  part  clean,  sharp,  coarse  sand.  The 
cost  per  foot  was  thirty-nine  cents,  including  all  excavation. 

A  similar  curb  at  Urbana,  111.,  was  4£  inches  thick  at  the 
top,  5  inches  at  the  base  and  7£  inches  high;  the  gutter  being 


1  W.  H.  Tarrant,  Engineer,  Proc.  111.  Soc.  Engr.  and  Surveyors,  1899. 


STREET  RAILWAY  FOUNDATIONS  433 

5  inches  thick  and  extending  18  inches  into  the  roadway.  The 
foundation  was  composed  of  eight  inches  of  cinders  or  gravel. 
The  concrete  was  of  one  part  Portland  cement  to  five  parts 
clean  gravel,  and  the  finishing  coat  was  one  inch  thick,  com- 
posed of  one  part  Portland  cement  to  two  parts  sharp  sand. 
The  price  per  linear  foot,  including  the  excavation,  removal  of 
old  curbing,  and  refilling,  was  forty-six  cents. 

At  South  Bend,  cement  curb  alone,  6  inches  wide  at  top, 
7  inches  at  bottom  and  16  inches  depth,  with  the  upper  half 
composed  entirely  of  one  to  two  Portland  cement  mortar,  has 
been  constructed  for  eighteen  cents  per  linear  foot. 

ART.  77.     STREET  RAILWAY  FOUNDATIONS 

659.  The  heavy  motor  cars  used  on  city  and  urban  electric 
railways  subject  the  track  to  very  severe  service.     As  the  head 
of  the  rail  must  be  practically  flush  with  the  pavement  on  city 
streets,  cross- ties,  when  used,  are  so  far  beneath  the  surface 
that  they  decay  rapidly  and  their  renewal  entails  the  tearing 
up  of  the  pavement.     As  there  is  not  the  same  necessity  for  a 
cross-tie  on  street  tracks  as  on  railroads,  since  the  rails  are  held 
to  gage  by  the  pavement,  these  objections  to  the  cross-tie  have 
led  to  the  adoption  of  a  concrete  girder  under  each  rail.     The 
rails  and  ties  (if  ties  are  used)  should  not  only  rest  upon  the 
concrete,  but  should  be  imbedded  in  it.     Track  in  which  the 
rails  rested  upon  concrete,  but  were  not  imbedded  in   it,  has 
been  found  to  yield  laterally  and  get  out  of  alinement,  while 
on  the  other  hand,  if  the  ties  rest  upon  earth  or  gravel  and  are 
filled  between  with  concrete,  the  track  is  likely  to  settle,  break- 
ing the  bond  of  the  concrete. 

660.  The  method  of  placing  concrete  beams  for  street  rail- 
way tracks  in  Minneapolis  was  as  follows : l  The  rails  were  first 
spiked  to  cross-ties  at  intervals  of  six  to  eight  feet,  and  the  rail 
joints  cast-welded.     In  laying  the  street  pavement  foundation 
of  natural  cement  concrete,  a  rough  groove,  fifteen  inches  wide 
at  the  bottom  and  eighteen  to  twenty  inches  at  the  top,  was 
left  under  each  rail.     This  groove  was  immediately  filled  be- 
tween ties  with  concrete  made  of  one  part  Portland  cement, 


1  F.  W.  Cappelen,  M.  Am.  Soc.  C.  E.,  Engineering  News,  Oct.  14,  1897; 
Municipal  Engineering,  November,  1896. 


434  CEMENT  AND  CONCRETE 

two  and  one-half  parts  sand,  and  four  and  one-half  parts  broken 
stone. 

The  rails  were  tied  together  every  ten  feet  with  wrought 
iron  tie  bars,  three-eighths  inch  by  two  inches,  set  on  edge.  These 
tie  bars  were  rounded  at  the  ends,  threaded  and  attached  to 
the  web  of  the  rail  by  two  nuts,  one  on  either  side  of  the  web. 
The  rails  were  then  spiked  to  the  concrete  beam,  the  temporary 
wooden  ties  removed,  and  the  spaces  left  by  them  filled  with 
concrete,  completing  the  beam.  As  the  concrete  beam  was 
eight  inches  thick  and  the  rail  five  inches,  the  sub-grade  was 
thirteen  inches  below  the  top  of  the  rail. 

On  the  gage  side  of  the  rail  were  placed  toothing  blocks  of 
granite,  3^  by  9  inches  by  4£  inches  deep,  held  away  from  the 
rail  1J  inches  by  temporary  wooden  strips.  After  removing 
these  strips,  cement  grout  was  poured  into  the  groove  to  fill 
2J  inches  over  the  base  of  the  rail,  the  remaining  2^  inches  to 
the  top  of  the  rail  being  filled  by  asphaltic  cement  which  re- 
mained soft  enough  to  permit  a  flange  groove  to  be  made  by  the 
first  car  over  the  track.  The  asphalt  wearing  surface  was  laid 
against  the  rail  on  the  outer  side.  Mr.  Cappelen,  in  describing 
this  construction,  says  that  a  rail  six  inches  high  with  six-inch 
base  should  be  used,  with  granite  toothing  blocks,  six  by  nine 
inches  by  five  and  one-half  inches  deep. 

The  cost  per  foot  of  rail  for  the  concrete  beam  construction 
only,  was  twenty-six  to  twenty-seven  cents,  and  for  the  filler, 
five  cents  per  foot.  The  cost  per  mile  of  double  track,  exclusive 
of  rails  and  pavement,  was  about  $8,670.00. 

Somewhat  similar  methods  have  been  employed  in  Toronto 
and  Montreal.  Canada,  Indianapolis,  Ind.,  and  Scranton,  Pa., 
Denver,  Detroit  and  Cincinnati. 

661.  At  Scranton,  Pa.,1  the  rails  were  laid  directly  on  the 
six-inch  concrete  base  of  the  pavement.  This  thickness  was 
increased  to  twelve  inches  under  the  joints  (which  were  rein- 
forced by  an  inverted  rail  four  feet  long)  and  under  steel  cross- 
ties  spaced  ten  feet  centers  and  formed  of  old  girder  rails  in- 
verted and  riveted  through  the  flanges  at  the  intersection. 
Flat  steel  tie  bars,  threaded  at  the  ends,  spaced  ten  feet  centers, 
were  also  used  here  as  at  Minneapolis. 


1  Description  of  the  systems  employed  in  several  cities  are  given  in  En- 
gineering News,  Dec.  26,  1901. 


STREET  RAILWAY  FOUNDATIONS  435 

The  concrete  mixing  plant  was  mounted  on  a  car  running 
on  the  track;  the  materials  were  delivered  to  the  machine  by 
hand  measuring  boxes,  and  the  Drake  mixer  deposited  the  con- 
crete directly  into  the  trench.  The  total  cost  per  foot  of  track 
is  given  as  $2.65,  $1.17  of  which  was  for  grading,  rolling,  con- 
creting and  brick  paving  at  $1.97  per  square  yard,  and  for  extra 
concrete  at  joints  and  ties  at  $0.72  per  square  yard. 

662.  At  Toronto,  Canada,  the  six-inch  concrete  base  of  the 
pavement  is  increased  to  eight  inches  in  thickness  for  twenty 
inches  width  under  each  rail,  and   the  base  of  the  latter  is  im- 
bedded one  inch  in    the  concrete.      A  6J-inch  grooved  girder 
rail  is  used,   with   mortar  rammed  between  the  web  and  the 
adjacent  paving  blocks. 

663.  At  Cincinnati  the    bottom  of  the  concrete  stringer  is 
nine  inches  below  the  base  of  the  nine-inch  grooved  girder  rail, 
and  the  concrete  is  built  up  from  three  to  six  inches  on  the  web, 
according  to  the  thickness  of  the  wearing  surface  of  the  pave- 
ment.    The  space  between  the  upper  part  of  the  web  and  the 
adjacent  paving  is  then  filled  with  cement  mortar,  thus  sup- 
porting the  head  of  the  rail  as  well  as  protecting  the  web  from 
corrosion. 


CHAPTER    XXI 

SPECIAL   USES   OF   CONCRETE   (CONTINUED).     SEWERS,  SUB- 
WAYS,   AND   RESERVOIRS. 

ART.  78.     SEWERS 

664.  There  seems  to  be  no  very  good  reason  why  concrete  is 
not  more  generally  employed  in  the  construction  of  all  large 
sewers.     With  sizes  less  than  two  or  two  and  one-half  feet  in 
diameter  the  difficulty  of  removing  the  centers  prohibits  the  use 
of  concrete  in  the  ordinary  way,  and  although  some  appliances 
have  been  devised  for  building  these  small  sewers  as  monoliths 
by  a  mold  that  advances  as  fast  as  the  concrete  is  tamped  in 
place,  they  have  not  proved  popular.     The  difficulty  of  obtain- 
ing a  perfect  grade,  and  the  undesirable  feature  of  leaving  the 
green  concrete  unsupported,  are  probably  reasons  sufficient  for 
this  lack  of  popularity. 

For  the  larger  size  sewers  concrete  has  several  advantages 
over  brick.  First  may  be  mentioned  the  very  smooth  finish 
that  may  be  obtained  on  the  invert,  appreciably  increasing  the 
velocity  of  flow  over  that  usually  obtained  with  brick  inverts. 
Cheaper  labor  may  be  employed  in  concrete  work  with  less 
danger  of  annoyances  from  strikes.  The  cost  is  from  one- 
third  to  one-half  less  than  for  brick. 

665.  METHODS  OF  CONSTRUCTION.  —  The  City  of  Washing- 
ton was  one  of  the  -  first  to  use    concrete  extensively  in  sewer 
construction1.     For  sizes  up  to  twenty-four  inches  internal  diam- 
eter  the  concrete  is  used    only  as  a  foundation    and   bedding 
for  the  ordinary  sewer  pipe.       For  a   twenty-four  inch  sewer 
the  pipe  rests  in  a  bed  of  concrete  twenty-seven  inches  wide 
at  the  bottom,  flaring  to  forty  inches  wide  at  the  level  of  the 
center  of  the  pipe,  and  then  carried  up  with  plumb  sides  for 
•six  inches,  and  finally  finished  by  planes  tangent  to  the  upper 

curve  of  the  pipe.     At  the  joints  there  are  bands  of  concrete 


1  Described  by  Capt.  Lansing  H.  Beach,  Corps  of  Engrs.,  U.  S.  A.  Report 
Operations  District  of  Columbia,  1895. 

436 


SEWERS  437 

extending  over  the  top,  so  that  at  these  places  the  pipe  is  en- 
tirely inclosed.  Similar  forms  are  used  for  the  smaller  sizes 
with  corresponding  decreased  dimensions.  For  all  sewers  be- 
tween ten  inches  and  twenty-four  inches  the  sub-grade  is  six 
inches  below  the  exterior  of  the  pipe,  and  in  all  cases  the  band 
about  the  joint  is  four  inches  thick  at  the  top. 

666.  The  method  of  laying  these  sewers  is  as  follows:  The 
trenches  are  2^  to  3  feet  in  width,  with  "  headers"  about  2   feet 
wide,   left    at  intervals  of   10  to   16  feet,   which   are    tunneled 
through.     The  grade  and  line  pegs  are  placed   in  the  headers 
at  the  ground  siarface,  and  a  cord  is  stretched  on  the  sewer  line 
over  at  least  four  stakes,   at  a   convenient  height  above  the 
grade,  and  thus  parallel  to  the  bottom  of  the  sewer. 

When  the  trench  is  to  the  required  grade,  a  six  inch  layer  of 
concrete,  made  with  one  barrel  natural  cement,  two  barrels 
sand  and  four  barrels  gravel,  is  placed.  This  concrete  is  rammed 
with  iron  rammers  weighing  sixteen  pounds,  and  having  eighteen 
square  inches  ramming  surface.  The  pipe  is  then  laid  upon 
this  bed  and  each  section  is  tested  for  line  and  grade.  For  the 
former,  a  plumb  bob  is  used  with  its  cord  held  against  the 
grade  cord  already  mentioned,  and  for  testing  the  grade  a  grad- 
uated pole  is  used,  with  a  projection  at  the  bottom  which  sets 
on  the  interior  of  the  pipe,  just  within  the  open  end. 

Concrete  is  then  lowered  in  buckets,  deposited  on  top  of 
the  pipe  and  allowed  to  fall  down  on  the  sides  so  as  not  to 
disturb  the  alinement.  When  enough  concrete  to  secure  the 
pipe  has  been  thus  placed,  it  is  rammed  and  the  concreting 
continued  until  the  required  form  is  obtained,  as  already  de- 
scribed. The  concrete  in  the  bands  carried  over  the  joints  is  not 
rammed  but  is  beaten  with  wooden  paddles  and  heavy  trowels  to 
compact  it  and  bring  it  to  the  desired  form,  four  inches  thick 
anc^  four  inches  wide  at  the  top,  and  flaring  to  twelve  inches 
wide  (in  the  direction  of  the  sewer)  at  the  top  of  the  pipe. 

667.  Cost.  —  The   quantities  of  concrete   materials   required 
to   lay   one   hundred    linear  feet    of    pipe  sewers  as    described 
above  are  given  as  follows :  — 

Size  of  sewer .8  inch  12  inch  18  inch  24  inch 

Cement,  bbls 6.76  10.58  14.77  19.14 

Sand,  cu.  yd 2.07  3.23  4.52  5.85 

Gravel,  cu.  yd 4.16  6.47  9.04  11.70 


438  CEMENT  AND  CONCRETE 

With  natural  cement  costing  $0.79  per  barrel  in  sacks,  sand 
$0.47  per  cu.  yd.,  gravel  $0.75  per  cu.  yd.,  and  laborers  $1.50 
to  $1.75  per  day,  foremen,  masons  and  inspectors  $4.00  per 
day,  the  average  cost  of  laying  pipe  sewers  in  this  manner  was 
approximately  as  follows,  exclusive  of  the  cost  of  the  pipe: 
8-inch,  $1.11;  12-inch,  $1.14;  15-inch,  $1.46;  18-inch,  $1.60; 
21-inch,  $1,67;  24-inch,  $2.32  per  foot. 

668.  Sewers  at  Chicago.  —  In  the  construction  of  some 
17,000  feet  of  sewers  for  the  Chicago  Transfer  and  Clearing 
Yards/  concrete  was  used  for  all  sewers  of  thirty-six  inches 
diameter  and  over.  The  excavation  was  mostly  in  blue  clay 
and  done  by  steam  shovel  to  a  depth  of  twenty  feet,  the  re- 
mainder being  removed  by  hand  shovels  and  swing  derrick. 
The  material  was  such  that  in  general  the  bottom  of  the  trench 
could  be  trimmed  to  the  form  of  the  exterior  of  the  sewer. 
The  thickness  of  the  ring  of  concrete  was  8  inches  for  36  and 
42-inch  sewers,  10  inches  for  48-inch,  and  12  inches  for  84  and 
90-inch  sewers. 

The  concrete  was  composed  of  one  part  "  Steel  Pozzolana" 
(slag)  cement,  three  parts  safld  and  five  parts  broken  stone. 
The  cement  was  of  course  very  finely  ground  and  showed  high 
seven-day  tests.  The  cost  was  $1.30  per  barrel  delivered. 
The  sand  was  the  Chicago  " torpedo"  sand,  coarse  and  of  good 
quality,  and  cost  about  ninety  cents  per  cubic  yard  delivered. 
The  stone  was  a  limestone  from  Summit,  111.,  crushed  in  two 
sizes,  namely,  1  to  2J  inches  and  £  to  1J  inches.  These  two 
sizes  of  stone  were  mixed  in  proportions  one  part  of  the  coarser 
to  two  of  the  finer.  The  cost  of  stone  was  about  $0.80  per 
cubic  yard  delivered. 

The  concrete  was  mixed  by  a  rotary  mixer  of  the  continuous 
type  provided  with  radial  blades.  The  mixer  was  mounted  on 
a  flat  car,  with  engine  and  upright  boiler.  Three  cars  of  stone, 
the  mixer  car,  two  cars  of  sand  and  one  of  cement  made  up  the 
concrete  train,  which  ran  on  a  track  laid  close  to  the  trench 
and  was  kept  near  the  work  by  a  small  locomotive.  The  mixer 
was  supplied  by  wheelbarrows  running  from  the  material  cars 
on  plank  runways  attached  to  the  cars.  The  concrete  was  also 
transported  in  wheelbarrows  from  the  mixer  to  the  trench. 


E.  J.  McCaustland,  Trans.  Assoc.  C.  E.,  Cornell  University,  1902. 


SEWERS  439 


The  bottom  of  the  trench  being  cut  to  form,  the  con- 
crete for  the  invert  was  laid  directly  on  the  sub-grade,  tamped  in 
layers  carried  up  until  the  invert  occupied  about  one  hundred 
forty  degrees  of  arc.  The  form  of  the  inner  face  of  the  invert 
was  maintained  by  template,  grade  stakes  being  set  12 \  feet 
apart  along  the  trench.  The  remainder  of  the  sewer  was  laid 
on  centers  resting  on  the  invert.  The  ribs  for  this  centering 
were  made  in  a  complete  circle,  of  three  thicknesses  of  one  by 
twelve  inch  boards  nailed  together  and  cut  to  a  true  circle. 
Ribs  were  placed  four  feet  center  to  center,  and  covered  with 
lagging  two  inches  thick  and  three  inches  wide,  planed  to  radial 
joints.  The  strips  of  lagging  were  held  in  place  at  each  end  of 
a  section  by  a  j\  by  2  inch  iron  band  passing  over  all  of  the 
strips,  and  turned  in  at  the  ends,  forming  a  hook  in  which  rested 
the  lower  lagging  strip,  the  other  strips  being  supported  by  this 
one.  The  lower  part  of  each  rib  rested  on  the  invert,  the  upper 
portion  being  cut  to  a  diameter  four  inches  less  (that  is,  smaller 
by  twice  the  thickness  of  the  lagging).  While  the  trench  was 
near  enough  to  the  outside  of  the  sewer  ring  not  to  measurably 
increase  the  amount  of  concrete  over  and  above  the  desired 
thickness,  the  trench  served  as  the  outside  form.  Above  this 
point,  planks  were  inserted  and  braced  to  the  sides  of  the  trench. 
From  the  haunches  to  the  crown  the  exterior  was  finished  with 
a  template. 

When  completed,  the  exterior  form  planks  were  removed, 
and  a  light  covering  of  earth  placed  on  the  surface  to  protect 
it  from  drying  too  rapidly.  This  was  especially  necessary  in 
this  case  on  account  of  the  kind  of  cement  used.  The  centers 
were  removed  usually  after  forty-eight  hours,  by  swinging  the 
ribs  about  the  vertical  diameter  and  removing  the  lagging.  As 
soon  as  the  centering  was  removed,  the  inner  surface  was  plas- 
ered  with  a  mortar  composed  of  three  parts  lake  sand  to  one 
part  cement. 

670.  Cost.  —  The  company  furnished  the  materials  used  in 
the  sewer  ring  and  manholes,  and  delivered  it  on  the  work, 
while  the  contractor  furnished  all  tools  and  labor  to  dig  the 
trenches,  complete  sewer  and  manholes,  and  do  the  back  filling. 
The  contract  prices  per  foot  are  given  by  Mr.  McCaustland,  the 
resident  engineer,  as  follows :  — 


440 


CEMENT  AND  CONCRETE 


36-inch  sewer  in  trench  averaging  11  feet  deep,  3,340  feet,  at  $2.30. 
42          "  "  "          14          "          2,660       "         3.00. 

48          "  "  "          17         "         4,540      "        3.57. 

84          "  "  "          22          "          1,000       "         5.91. 

90          "  "  "          24          "          5,400       "         6.68. 

From  the  data  given  we  have  computed  the  approximate 
quantities  of  concrete  per  foot  of  sewer,  and  assuming  the  cost 
of  the  materials  for  a  cubic  yard  at  $3.00,  we  obtain  the  follow- 
ing approximate  costs:  — 


MATERIALS. 

SIZE 
SKWER. 

DEPTH 
TRENCH. 

CONSTRUCTION 
CONTRACT 
PRICE  PER 
FOOT. 

ESTIMATED 
TOTAL  COST 
PER  FOOT. 

Approximate 
Cubic  Yards 

Approximate 
Cost 

Concrete. 

Concrete. 

36  in. 

11  feet. 

.285 

$  .85 

$2.30 

$3.15 

4'2  " 

14    " 

.325 

.97 

3.00 

3.97 

48  " 

17     " 

.47 

1.41 

3.57 

4.1)8 

84" 

22    " 

.93 

2.79 

5.91 

8.70 

90" 

24    " 

.99 

2.97 

6.68 

9.65 

671.  Special  Molds  for  Small  Sewers.  —  In  the  construction 
of  a  thirty  inch  sewer  at  Medford,  Mass.,1  Mr.  William  Gavin 
Taylor  invade  use  of  a  very  convenient  form.     The  lower  240 
degrees  of  the  sewer  was  of  concrete,  the  upper   120  degrees 
being  of  brick.     To  construct  the  concrete  portion  as  a  mono- 
lith, the  forms  were  constructed  in  lengths  of  ten  feet,  separat- 
ing on  a  vertical  line  into  two  halves.     The  two  halves  were 
connected  by  clamps,  and  held  at  the  proper  distance  apart  by 
dog  irons  in  the  end  ribs  of  each  form.     After  smearing  the 
forms  as  usual,  the  concrete  was  deposited  and  rammed.     When 
it  had  partially  set,  the  dog  irons  were  removed  and  turn-buckles 
used  to  slowly  pull  the  two  halves  together.     This  method  pre- 
vented the  green  concrete  being  broken,  although  the  concrete 
extended  up  on  the  sides  thirty  degrees  above  the  horizontal 
diameter. 

672.  The  centers  used   for  the  brick  arch  were  also    ingen- 
iously arranged,  and  since  they  might  have  been  used  for  a  con- 
crete arch  they   may  be  described  here.     These   centers   were 
also  in  ten  foot  lengths.     The  ribs,   of  two  inch  plank,   were 


1  Abstract  from  Annual  Report  of  City  Engineer,  Engineering  Record, 
Nov.  7,  1903. 


SEWERS  441 

spaced  two  feet  centers,  with  lagging  J  inch  thick  by  1£  inch 
wide,  with  one  bevel  edge  to  make  a  tight  upper  surface.  The 
rear  end  of  each  center  was  supported  by  wedges  securely 
fastened  to  the  outer  end  of  the  preceding  section,  the  forward 
end  being  supported  by  a  screw  jack. 

After  turning  the  arch,  these  centers  were  removed  by  the 
aid  of  a  special  truck  the  axles  of  which  were  bent  at  such  an 
angle  as  to  make  the  cast  iron  wheels  fit  the  concrete  invert. 
The  axle  of  a  roller  was  first  fastened  to  the  outer  rib  of  the 
center  to  be  removed;  the  truck  was  then  run  back  a  foot  or  so 
under  the  center  and  the  screw  jack  supporting  the  forward 
end  of  the  center  released.  This  allowed  the  forward  end  to 
drop  a  short  distance,  the  roller  resting  on  the  running  board 
of  the  truck.  The  latter  was  then  pulled  into  the  sewer  far 
enough  to  let  the  roller  run  off  the  end  of  the  truck  and  lock 
itself.  The  truck  being  then  pulled  out  of  the  sewer  toward 
the  finished  end,  drew  the  center  away  from  the  wedges  sup- 
porting the  rear  end,  allowing  the  form  to  drop  on  the  truck 
and  be  wheeled  out  of  the  sewer.  By  this  method  the  centers 
were  successfully  removed  without  injuring  the  concrete. 

673.  Cost.  —  From   data   given,    the   cost   of    this   sewer  — 
about   sixteen   hundred   feet   in   length  —  is   approximately   as 
follows,  labor  costing  twenty-five  cents  an  hour:  - 

1.25  cu.  yds.  excavation  and  back  fill,  at  $.59 $0.74 

.15  cu.  yd.  concrete,  at  $6.70       1.00 

.037  cu.  yd.  brick  masonry,  at  $12.05 44 

Cost  of  linear  foot,  exclusive  of  manholes,  estimated  at  .    .   $2.18 
The  total  cost  per  linear  foot  is  given  as $2.39 

674.  New  York  Sewers.  —  In   connection  with  the  construc- 
tion of  the   New   York   Rapid   Transit   Railway,   some   of  the 
sewers  were  built  of  concrete.     This  work  was  done  with  ex- 
ceptional care,  and  on  a  large  scale,  and  it  was  found  that  the 
concrete  sewers  cost  one-third  less  than  similar  sewers  of  brick. 

The  method  of  construction  of  one  section  may  be  described 
as  follows : l  The  forms  for  the  invert  of  the  straight  lengths 
of  sewer  were  twelve  feet  in  length,  consisting  of  a  strong  frame- 
work covered  with  closely  matched  lagging,  planed  smooth  and 


Engineering  News,  March  6,  1902. 


442  CEMENT  AND  CONCRETE 

greased  with  machine  oil.  After  the  trench  was  prepared,  con- 
crete was  placed  and  rammed  until  the  top  of  the  concrete  was 
within  about  one-half  inch  of  the  flow  line  of  the  invert.  To 
accomplish  this,  a  straight  edge  was  used,  bearing  on  the  fin- 
ished invert  in  the  rear  and  a  template  secured  to  the  trench 
timbering  just  ahead  of  the  section  under  construction. 

The  invert  centers  were  then  placed,  resting  on  the  finished 
invert  at  the  rear  and  on  a  solid  foundation  accurately  set  to 
grade  at  the  forward  end.  Mortar  composed  of  equal  parts 
Portland  cement  and  sand  was  then  tamped  between  the  invert 
form  and  the  bottom  concrete  already  laid.  When  the  flow 
line  had  been  thus  accurately  formed,  the  center  was  braced 
and  vertical  planking  set  to  form  the  outside  of  the  walls.  The 
concrete  was  then  rammed  in  place. 

Joists  of  two  inch  by  four  inch  scantling  laid  along  the 
center  of  the  top  of  each  side  wall  of  the  invert  section,  formed, 
when  removed,  a  mortise  into  which  the  fresh  concrete  of  the 
arch  section  was  rammed  to  form  a  bond.  Similar  mortises 
were  also  made  in  the  forward  end  of  each  section  as  built. 
After  twenty-four  hours  or  more  the  forms  were  removed,  and 
a  thin  cement  wash  was  applied  to  the  interior,  sufficient  only 
to  fill  any  slight  imperfections  in  the  surface. 

The  arch  centers,  similar  in  construction  to  the  forms  for 
the  invert,  were  put  in  place  and  plastered  with  one  inch  of 
rich  Portland  mortar.  Concrete  was  then  placed  sufficient  to 
make  the  arch  eight  inches  thick,  the  outside  of  the  walls  being 
formed  by  inclined  boards  braced  to  the  trench,  and  the  top  of 
the  extrados  was  formed  by  hand. 

675.  Steel  Forms.  —  Two  novel  types  of  centering  have  been 
devised,  in  which  the  surface  next  the  concrete  is  of  steel.  In 
one  of  these  *  the  forms  are  in  sections  about  three  feet  long. 
Two  of  the  pieces  of  steel  are  of  a  width  suitable  to  reach  from 
the  bottom  of  the  sewer  to  just  above  the  spring  line  of  the 
arch,  while  a  third  piece  forms  the  arch  center.  The  strips  are 
bent  at  an  acute  angle  at  the  sides,  thus  projecting  into  the 
sewer  along  an  element  of  the  surface  where  the  plates  join  ;  the 
two  sides  of  adjacent  plates,  which  flare  away  from  each  other, 
are  then  connected  by  a  continuous  U-shaped  clip  of  steel  slipped 


Engineering  Record,  Jan.  9,  1904. 


SUBWAYS  AND   TUNNELS  443 

on  from  the  end  of  a  three  foot  section,  and  the  intervening 
space  in  the  clip  filled  with  clay  or  melted  paraffin.  The  form  is 
assembled  outside  the  trench,  and  after  the  paraffin  is  in  place, 
the  center  may  be  handled.  When  the  sewer  is  completed, 
the  paraffin  is  melted  by  a  suitable  heater,  or  the  clay  is  washed 
out,  and  the  form  may  be  collapsed  and  removed. 

676.  In  the  other  form  l  the  steel  plates  are   in   continuous 
strips  about  six  inches  wide  and  are  applied  by  setting  up  the 
wooden  form  on  an  improvised  axis,  revolving  the  form  and 
wrapping  the  steel  sheet  about  it  as  it  is  revolved.     The  wooden 
form  is  in  two  parts,  upper  and  lower,  firmly  connected  while 
in  use,  but  the  two  parts  may  be  made  to  approach  each  other 
by  driving  out  the  wedges  between  them.     After  the  winding, 
the  center,  with  its  sheet  steel  jacket,  is  lowered  into  the  trench. 
When   the   concrete   is   completed,   the   form   is   collapsed   and 
removed,  leaving  the  spiral  of  steel  in  place  to  support  the  con- 
crete until  the  latter  is  well  set.     The  steel  is  then  removed  by 
simply  pulling  on  one  end.     As  it  comes  away  from  the  concrete 
it  is  wound  into  a  coil,  and  is  then  ready  to  be  rewound  on  the 
wooden  form.     Both  of  the  above  styles  have  been  patented. 

ART.  79.     CONCRETE  SUBWAYS  AND  TUNNEL  LINING 

677.  The   advantages   of   concrete   in   subway   construction 
and  in   tunnel   lining  are  now   well  established.     In  subways 
built  in  open  cut,  the  side  walls  and  invert  are  of  concrete  built 
in  place,  while  the  roof  is  frequently  made  with  I-beams  with 
concrete  arches  turned  between  them.     The  I-beams  are  sup- 
ported directly  on  the  side  walls,  which  are  usually  made  mono- 
lithic with  the  invert. 

678.  Special  precautions  have  to  be  taken  to  exclude  water 
from  a  subway,  and  for  this  purpose  tarred  felt  and  Portland 
cement  plaster  are  employed. 

The  specifications  for  the  New  York  Rapid  Transit  Subway  2 
were  carefully  framed  to  secure  a  waterproof  construction.  On 
the  sub-grade  was  placed  a  layer  of  concrete,  smooth  and  level 
on  top.  This  was  covered  by  alternate  layers  of  hot  asphalt 
and  felt,  from  two  to  six  layers  of  each  being  used  as  deemed 


1  Engineering  News,  Feb.  18,  1904. 

2  Abstracted  in  Engineering  News,  Feb.  13,  1903. 


444  CEMENT  AND  CONCRETE 

necessary  for  the  conditions  encountered.  The  remainder  of 
the  concrete  forming  the  floor  was  then  laid  upon  the  top  layer 
of  asphalt.  In  dry,  open  soil  the  felt  was  not  required,  and  in 
dry  rock  excavations  above  water  level  both  the  asphalt  and 
felt  were  omitted.  Similar  provisions  were  made  for  water- 
proofing the  side  walls  and  roof,  resulting  in  a  complete  layer 
of  asphalt  and  felt  imbedded  in  concrete  about  the  entire  tun- 
nel, the  waterproofing  being  protected  both  inside  and  out  by 
concrete. 

679.  In  the  construction  of  the    Boston  Subway  l  the  por- 
tion built  in  open  cut  was  made  as  follows:  The  work  was  di- 
vided into   sections   of   convenient  length,   about  twelve  feet, 
so  that  work  on  a  section  could  be  carried  on  continuously  until 
completed.     Upon  the  prepared  grade  were  laid  three  thick- 
nesses of  tarred  felt  with   six-inch  lap  joints,  well  pitched  be- 
tween the  layers,  and  the  top  of  the  upper  layer  thoroughly 
covered  with  the  pitch.     When  the  latter  had  hardened,   the 
invert  was  laid  over  the  entire  width  of  the  section. 

At  each  side  a  back  wall  six  inches  thick  was  built  up  to  a 
convenient  height  and  braced.  The  forms  were  then  removed 
and  the  face  of  this  back  wall  was  plastered  with  rich  Portland 
cement  mortar.  The  main  side  walls  were  then  built  up  be- 
tween this  layer  of  plaster  and  the  forms  defining  the  interior 
face  of  the  wall.  This  portion  of  the  subway  had  an  arch 
roof,  two  feet  thick  at  the  crown,  which  was  laid  on  wooden 
centers.  The  exterior  of  the  roof  was  plastered  like  the  side 
walls,  and  then  covered  with  four  inches  of  concrete  to  protect 
the  plaster  from  injury.  The  centers  were  removed  after  from 
ten  to  thirty  days;  the  span  of  the  arch  was  about  twenty- 
three  feet. 

680.  Tunnel  Lining  in  Firm  Earth.  —  In  building  tunnels  in 
earth  that  is  sufficiently  firm  not  to  require  extensive  timber- 
ing, concrete  is  well  adapted  for  lining.     An  instance  of  this  is 
furnished  by  the  extensive  system  of  tunnels  constructed  for 
telephone  and  telegraph  service  under  the  streets  of  Chicago.2 
The  trunk  conduits  for  this  system  are  about  thirteen  by  four- 


1  Annual  Report  Boston  Transit  Commission,  1900;  also  described   in 
Engineering  News,  April  4,  1901. 

2  Mr.  George  W.  Jackson,  Engineer,  Proc.  W.  Soc.  Engrs.,  1902;  also  in 
Engineering  News,  Feb,  19,  1903. 


SUBWAYS  AND   TUNNELS  445 

teen  feet  inside,  and  the  laterals  about  six  by  seven  feet,  all  of 
the  five  center  horseshoe  form. 

The  excavation  was  in  hard  clay  which  stood  up  well.  Shafts 
were  located  in  basements  of  buildings  rented  for  the  purpose, 
and  in  these  basements  were  placed  the  compressed  air  plants, 
material  bins,  concrete  mixers,  etc.  The  large  air  locks,  some 
of  which  would  hold  ten  small  construction  cars,  were  placed 
at  the  bottoms  of  the  shafts.  Work  was  done  in  three  shifts, 
working  eight  hours  each.  The  two  night  shifts  could  excavate 
about  twenty-one  feet  of  lateral  tunnel  in  the  sixteen  hours, 
and  the  day  shift  placed  the  lining. 

681.  The  concrete  was  in  general  composed  of  five  parts  of 
broken  stone  and  screenings,  or  of  mixed  gravel  and  sand,  to 
one  part  Portland  cement.  For  intersections  but  four  parts 
aggregate  were  used.  This  should  make  a  very  strong  concrete. 
The  centers  for  the  smaller  conduits  were  made  of  three-inch 
channels,  each  rib  being  in  five  parts  bent  to  the  proper  form 
and  connected  by  flange  plates  bolted  to  the  inside  of  the  chan- 
nels at  the  ends.  These  ribs  were  placed  three  feet  apart,  and 
two-inch  plank  used  for  lagging. 

The  ribs  for  the  trunk  sewers  were  of  similar  construction, 
but  with  heavier  channels  braced  with  angles.  Steel  lagging 
was  used,  made  of  plates  about  twelve  by  thirty-six  inches, 
stiffened  by  1^  inch  angles  on  four  edges.  There  were  also 
provided  bulkheads  or  steel  end  plates  of  voussoir  shape,  twelve 
inches  along  the  intrados  and  twenty  inches  high,  for  the  pur- 
pose of  retaining  the  end  of  each  section  of  lining  and  permit 
thorough  tamping.  These  bulkhead  sheets,  or  "end  flights," 
were  also  stiffened  along  three  edges,  and  could  be  attached  to 
the  webs  of  the  channel  ribs  by  short  bolts. 

The  concrete  was  mixed  at  the  shaft  head  and  conveyed  to 
the  work  in  cars  twenty  inches  wide  and  four  feet  long,  running 
on  a  fourteen-inch  gage  track.  The  floor  of  the  tunnel  was 
first  laid  in  the  excavation,  the  steel  ribs  then  put  in  place  on 
the  floor,  and  the  lagging  placed  at  the  bottom  and  built  up 
the  sides  just  ahead  of  the  concrete.  When  near  the  crown, 
short  pieces  of  lagging  three  feet  in  length  covering  but  two 
ribs  were  used,  and  the  concrete  rammed  in  from  the  end  of 
these  short  sections  until  they  were  complete,  and  then  another 
row  of  short  pieces  placed  and  the  operations  repeated. 


446  CEMENT  AND  CONCRETE 

The  concrete  floor  of  laterals  was  designed  to  be  thirteen 
inches,  and  the  sides  and  arch  ten  inches  thick,  but  in  all  cases 
the  entire  space  between  the  lagging  and  the  sides  of  the  ex- 
cavation was  filled  with  concrete. 

682.  In  such  work  as  this  only  the  best  materials  should  .be 
used,   and,   as  early  strength  is   desired,   the   use   of  Portland 
cement  is  general  in  order  that  the  centers  may  be  removed 
within   a   reasonable   period.     The   ends    of   the   sections   into 
which  the  work  is  divided  should,  if  possible,  be  brought  up 
square,  the  bulkhead  sheets  described  above  being  an  ingenious 
and  effective  method  of  providing  for  this.     Where  it  is  not 
practicable  to  finish  with  a  square  end  over  the  entire  area  of 
section,   then  the  work  on  the  sides  should  be  stepped  back 
from  the  bottom  toward  the  crown,  each  step  being  bounded 
by  planes  corresponding  to   coursing  and  heading  joints  in  a 
masonry  arch. 

683.  Tunnel  Lining  in  Soft  Ground.  —  For  tunnels  in  soft 
ground  requiring  the  use  of  a  shield,  some  difficulties  in  using  a 
concrete  lining  are  apparent.     The  principal  one  of  these  lies 
in  the  fact  that  the  fresh  concrete  is  not  capable  of  taking  the 
thrust  of  the  jacks  used  in  forcing  the  shield  ahead.     Attempts 
have  been  made  to  overcome  this  difficulty  by  so  constructing 
the  centers  that  the  jacks  may   bear  against  them  instead  of 
on  the  fresh  concrete. 

Another  difficulty  is  that  in  materials  requiring  almost  con- 
tinuous support,  the  temporary  timbering  is  in  the  way  of  the 
centering  for  the  concrete  construction;  and  still  another  is  the 
difficulty  of  properly  tamping  the  arch  at  the  crown  where  the 
tail  of  the  shield  confines  the  working  space.  Concrete  blocks 
were  tried  in  the  construction  of  sewers  in  Melbourne,  but 
without  entire  success.  Such  blocks  were  successfully  em- 
ployed in  the  underground  road  system  of  Paris,  though  at- 
tempts to  use  fresh  concrete  in  shield  tunneling  for  this  work 
proved  a  failure. 

684.  East  Boston  Tunnel. — In  the  construction  of  the  East 
Boston  Tunnel  Extension  of  the  Boston  Subway,  however,  a 
monolithic  concrete  lining  has  been  successfully  built,  the 
tunnel  being  excavated  by  shield. 

This  tunnel  is  about  twenty  by  twenty-four  feet  for  double 
track  electric  line,  The  arch  ring  and  the  walls  are  thirty- 


SUBWAYS  AND   TUNNELS  447 

three  inches  in  thickness,  while  the  invert  is  twenty-four  inches. 
Two  side  drifts,  eight  feet  square,  were  first  driven  a  certain  dis- 
tance and  timbered.  The  bottoms  of  these  drifts  were  then 
excavated,  and  the  side  foundations  of  concrete  were  placed  in 
lengths  of  sixteen  to  twenty  feet.  When  the  foundations  had 
set,  the  interior  forms  for  the  side  walls  were  placed  upon  them, 
supporting  the  caps,  the  exterior  plumb  posts  removed,  and 
the  concrete  side  walls,  three  feet  thick,  built  up  to  within 
sixteen  inches  of  the  springing  line  of  the  arch.  This  work  was 
kept  about  one  hundred  feet  in  advance  of  the  shield. 

The  shield,  provided  with  live  rollers,  rested  upon  these  side 
walls,  the  rollers  running  in  a  flanged  plate  placed  on  top  of  the 
walls.  The  shield  was  forced  ahead  thirty  inches  at  a  time, 
and  sections  of  the  arch  thirty  inches  in  length  were  turned 
directly  behind  the  shield. 

685.  The  centers  of  the  arch  were  of  curved,  ten  inch  steel 
channels  spaced  thirty  inches  apart,  and  the  lagging,  four 
inches  thick,  was  placed  from  the  bottom  toward  the  key  as 
the  concrete  was  built  up.  Each  section  of  arch  is  keyed  with 
concrete  pressed  through  two  holes  in  the  rear  girder  at  the 
top  of  the  shield,  special  rammers  being  used  to  tamp  the  con- 
crete into  the  space  at  the  crown  of  the  arch,  the  concrete  being 
directed  into  place  by  curved  sheet-iron  troughs. 

In  each  section  of  arch  sixteen  cast  iron  bars,  three  and  one- 
quarter  inches  in  diameter  and  thirty  inches  long,  are  built 
into  the  concrete  in  position  to  receive  the  thrust  of  the  shield 
jacks.  Wooden  bulkheads  on  the  jack  plungers  serve  to  con- 
fine the  fresh  concrete,  but  the  reaction  is  taken  on  the  cast 
iron  bars  which,  being  butted  end  to  end  in  successive  sections 
of  the  arch,  carry  the  stress  back  to  concrete  that  is  able  to 
sustain  it.  As  the  shield  advanced,  the  space  left  over  the 
completed  arch  by  the  tailpiece  of  the  shield  was  filled  with 
grout  under  pressure.  The  centers  remained  in  place  thirty 
days.  The  invert  was  excavated  and  laid  in  ten-foot  sections 
about  twenty-five  feet  in  the  rear  of  the  shield.  The  concrete 
was  mixed  at  the  bottom  of  the  shaft  and  passed  through  the 
air  lock  on  cars.  The  concrete  cars  ran  on  a  higher  level  than 
the  muck  cars,  in  order  not  to  interfere  with  the  excavation. 

686.    Lining  Tunnels  in  Rock.  —  If  the  rock  through  which 
a  tunnel  is  driven  is  seamy  and  insecure,  concrete  is  in  most 


448  CEMENT  AND  CONCRETE 

cases  the  cheapest  and  best  lining.  The  cost  of  the  lining  is, 
of  course,  less  if  it  can  be  built  in  connection  with  the  excava- 
tion, but  it  is  frequently  difficult  to  foresee  how  a  given  rock 
will  stand  exposure  to  the  air  and  water,  and  it  becomes  an 
exceedingly  nice  question  to  determine  at  the  time  of  building 
a  tunnel  whether  lining  is  required.  In  many  cases  this  ques- 
tion is  settled  in  the  affirmative  by  other  considerations  than 
the  character  of  the  rock,  as  the  resistance  to  flow,  in  water- 
works and  sewers,  or  the  ease  of  ventilation  and  the  necessity 
of  a  good  appearance,  as  in  street  or  steam  railway  tunnels. 

687.  New  York  Subway.  —  In  the  construction  of   portions 
of  the  rapid  transit  subways  of  New  York,  a  traveling  center 
which  served  also  to  support  a  working  platform  was  carried 
on  six  wheels  running  on  a  track  laid  on  the  footing  courses  of 
the  side  walls.     This  center  carried  at  the  side,  sections  of  lag- 
ging curved  to  the  required  form  of  the  side  walls.     This  lagging 
was  adjusted  in  place,  and  braced  from  the  platform  or  center 
by  means  of  wedges.     Directly  behind  this  traveling  center  was 
a   similar   platform   carrying   a   derrick;   and   behind   this,   the 
traveling  center  carrying  the  lagging  for  the  roof.     This  third 
platform  was  jacked  up  to  place  the  roof  lagging  at  the  correct 
elevation,  and  firmly  supported  by  wedges. 

The  concrete  was  brought  in  skips  on  cars  that  ran  on  the 
floor  level  and  stopped  beneath  the  derrick  platform.  The 
derrick  hoisted  the  skips  through  a  hole  in  the  platform  and 
placed  them  on  cars  on  either  the  side  wall  or  the  roof  platform, 
so  that  the  concrete  was'  delivered  either  to  the  side  wall  forms 
in  advance,  or  the  roof  forms  in  the  rear  as  required.  The 
concrete  was  rammed  in  a  direction  transverse  to  the  tunnel 
axis  until  the  roof  was  completed,  except  for  a  space  about 
five  feet  wide  at  the  crown.  The  arch  was  then  keyed  by 
tamping  the  concrete  in  from  the  end  of  the  form.  The  two 
platforms  carrying  the  forms  were  each  forty  feet  long,  and 
the  derrick  platform  was  eighteen  feet. 

688.  The  excavated  rock  was  crushed  for  the  concrete  on  a 
working   platform    erected   over   and    around   the   shaft   head. 
Cars  delivered  the  excavated  material  at  the  shaft  in  steel  skips, 
which  were  hoisted  to  the  working  platform,  set  on  push  cars 
and  dumped  into  bins,  from  which  stone  was  delivered  to  the 
crusher;  these  cars  then  passed  under  the  crushed  stone  bins, 


SUBWAYS  AND   TUNNELS  449 

were  loaded  with  broken  stone,  run  back  to  the  shaft  head, 
and  the  broken  stone  dumped  into  bins  mounted  over  the 
mixer.  The  skips  were  then  lowered  into  the  shafts  by  the 
derricks,  to  be  run  to  the  headings  and  reloaded.  The  stone 
and  sand  were  fed  to  a  measuring  box  by  means  of  a  hopper, 
the  measuring  box  discharging  directly  into  a  cubical  mixer, 
which  was  high  enough  above  the  tunnel  floor  to  dump  directly 
into  skips  on  the  cars. 

689.  Cascade  Tunnel.  —  In  the  construction  of  the  Cascade 
Tunnel  of  the  Great  Northern  Railway    a   somewhat  different 
arrangement  was  used. 1     The  working  platform  in  the  tunnel 
was  erected  five  hundred  feet  in  length,   and  cars  hauled  by 
cable  up  an  incline  to  the  platform.     The  side  walls  were  built 
in  alternating  sections,  eight  to  ten  feet  in  length,  the  support 
of  the   arch   timbering  being  thus  gradually   transferred  from 
the  plumb  posts  to  the  concrete  of  the  side  walls.     Arch  sections 
were  built  in  twelve  foot  lengths,  the  centers  being  made  of 
four  by  sixteen  inch  plank  without  radials,  so  as  to  leave  a 
clear   way   for   concrete   cars   on   the   working   platform.     The 
latter  were  high  enough  to  allow  the  material  cars  to  run  be- 
neath them. 

690.  Concrete  vs.  Brick.  —  There   are  frequent  instances  in 
engineering  construction  where  brick  masonry  might  well  have 
been  replaced  by  concrete,  and  the  use  of  brick  for  tunnel  lining 
is  still  adhered  to  in  many  cases.     This  is  partly  because  some- 
what less  elaborate  centers  can  be  used  for  brick  arches,  and 
the  centers   may   be  struck  somewhat  earlier,   and   partly  be- 
cause  of  extreme   conservatism   on   the   part  of  the   designer, 
although  without  doubt  there  are  cases  where  the  use  of  brick 
is  entirely  warranted. 

An  interesting  instance  of  the  greater  adaptability  of  con- 
crete under  unforeseen  conditions,  however,  is  presented  by  the 
Third  Street  concrete  and  brick  lined  tunnel  at  Los  Angeles, 
Cal.2  This  tunnel  was  excavated  mostly  through  an  argilla- 
ceous sandstone.  The  side  walls  were  of  concrete  up  to  the 
haunches,  the  upper  part  of  the  arch  being  of  six  courses  of 
brick.  A  streak  of  yellow  clay  was  encountered,  and  it  "was 

1  Mr.  John  F.  Stevens,  M.  Am.  Soc.  C.  E.,  Engineering  News,  Jan.    10, 
1901. 

2  J.  H.  Quinton,  M.  Am.  Soc.  C.  E.,  Engineering  News,  July  18,  1901. 


450  CEMENT  AND  CONCRETE 

soon  demonstrated  that  the  six  ring  brick  arch,  which  occupies 
the  central  portion  of  the  roof,  was  not  strong  enough  to  hold 
up  the  immense  weight  above  it,  and  the  temporary  timbering 
was  crushed  and  broken  in  a  most  alarming  way."  The  strength 
of  the  arch  was  increased  by  using  nine  rows  of  brick  instead 
of  six  until  the  clay  seam  was  passed.  In  such  portions  of  the 
six  ring  arch  as  had  cracked,  it  was  found  that  the  inner  ring 
of  brickwork  had  separated  from  the  second  ring,  and  in  places 
the  second  .ring  had  separated  from  the  third.  The  concrete 
walls  had  shown  no  evidence  of  weakness. 

To  repair  the  brickwork,  steel  concrete  beams  or  arches  were 
inserted  in  the  brickwork  at  intervals  of  four  feet,  and  extend- 
ing from  one  concrete  wall  to  the  other.  These  beams  were 
twrelve  inches  wide  and  eight  to  twelve  inches  deep,  made  of 
rich  concrete,  and  had  imbedded  in  each  beam  two  pieces  of 
three  inch  by  three-quarter  inch  steel.  The  steel  ribs  were  set 
in  recesses  cut  out  of  the  brickwork,  and  rested  at  the  ends  upon 
the  concrete  of  the  side  walls.  Substantial  centers  were  used 
for  building  the  concrete  beams,  and  when  the  latter  had  set, 
the  defective  brickwork  between  adjacent  beams  was  cut  out 
and  replaced  by  rich  concrete. 

691.  Aspen  Tunnel.  —  Another  illustration  of  the  adaptabil- 
ity of  concrete  when  unexpected  difficulties  arise,  is  furnished 
by  the  construction  of  the  Aspen  Tunnel  on  the  Union  Pacific 
Railroad. l     The  original  design  provided  for  sets  of  timbers  to 
support  the  excavation,  spaced  about  three  feet,  center  to  center, 
but  for  nine  hundred  feet  of    the  tunnel  such  pressures  were 
encountered  that  in  places  a  solid  wall  of  twelve  by  twelve  inch 
timber  was  forced  in.     For  a  portion  of  this  section  the  lining  was 
built  of  a  combination  of  concrete  with  steel  ribs.      The  latter 
were  12-inch,  55-pound  I-beams  spaced  from  twelve  to  twenty- 
four  inches,  center  to  center,  curved  to  conform  to  the  interior 
of  the  tunnel.     The  concrete  was  built  up  around  and  between 
the  beams,  the  inner  flange  being  covered  by  from  four  to  seven 
inches,  and  the  total  thickness  of  the  walls  two  to  three  feet. 

692.  The  Perkasie  Tunnel  of  the  Philadelphia  and  Reading 
Railroad  was  constructed  through  a  firm  rock,  which,  however, 
was  intersected  by  several  strata  of  seamy  rock.     As  trouble 


1  W.  P.  Hardesty,  Engineering  News,  March  6,  1902. 


SUBWAYS  AND  TUNNELS  451 

was  experienced  from  rock  falling  from  these  strata,  it  was 
decided  to  line  the  tunnel  at  such  places.  This  lining  had  a 
minimum  thickness  of  eighteen  inches  at  the  crown  and  twelve 
inches  at  the  sides.  Traffic  through  the  tunnel  was  not  ob- 
structed during  the  work  of  placing  the  lining.  In  laying 
about  five  hundred  cubic  yards  of  concrete,  the  cost  was  about 
ten  dollars  and  eighty  cents  per  cubic  yard,  exclusive  of  cost 
of  centering  and  dry  filling.1 

693.  Water  Works  Tunnel.  —  The  lining  of  portions  of  the 
Beacon  Street  Tunnel  of  the  Sudbury  River  Aqueduct  was 
undertaken  some  fourteen  years  after  its  excavation,  and  at  a 
time  when  it  was  necessary  to  use  the  tunnel  intermittently  to 
supply  water  to  the  city  of  Boston.  The  methods  employed 
are  described  by  Mr.  Desmond  FitzGerald  in  Transactions 
American  Soc.  C.  E.  for  March,  1894. 

A  substantial  track  of  2  feet  1J  inch  gage  was  laid  from  a 
manhole  furnishing  access  to  the  sewer  to  the  portion  of  the 
tunnel  to  be  lined.  The  rails',  weighing  thirty-six  pounds  to 
the  yard,  were  supported  on  small  but  substantial  trestles, 
built  of  three  by  four  inch  spruce  joists,  and  placed  eight  feet 
between  centers.  Every  third  trestle  was  braced  from  the 
sides  and  roof  of  the  tunnel  to  prevent  the  track  being  floated 
when  the  tunnel  was  in  use.  The  trestles  also  carried  five  rows 
of  planks  for  the  workmen  to  walk  on  in  pushing  the  cars. 
The  track  was  elevated  by  these  trestles,  so  the  work  was  not 
seriously  interfered  with  by  a  small  amount  of  water  in  the 
tunnel.  The  track  cost  about  eighty-seven  cents  a  foot. 

Cars  to  run  on  these  tracks  to  deliver  materials  and  concrete 
had  frames  five  feet  by  one  foot  nine  inches,  with  twenty  inch 
wheels,  and  cost  about  fifty-six  dollars  each. 

694.  Centers.  —  The  centers  were  in  three  parts,  two  for 
side  walls  and  one  for  roof.  The  ribs  were  of  three  thicknesses 
of  two  by  ten  spruce  plank,  without  interior  bracing  for  the 
roof  section.  The  side  sections  had  each  an  inclined  brace. 
Wedges  were  inserted  between  the  tops  of  the  side  sections 
and  the  bottoms  of  the  roof  ribs  to  hold  the  latter  in  place. 
The  lagging  was  two  by  four  inch  spruce,  in  eight  foot  lengths, 
with  beveled  edges  and  planed  both  sides.  The  centers  .were 


P.  D.  Ford,  M.  Am.  Soc.  C.  E.,  Trans.  A.  S.  C.  E.,  March,  1894. 


452  CEMENT  AND  CONCRETE 

spaced  four  feet  apart,  and  seventy-five  full  centers  were  built; 
these,  with  the  lagging,  contained  14,000  feet  B.  M.  of  lumber, 
and  cost  $1,460.55,  or  $104.30  per  thousand  feet  B.  M. 

695.  Methods  of  Work.  —  Broken  stone,  sand  and  cement 
were  stored  in  shanties  over  and  around  the  manhole  leading 
to  the  tunnel,  and  arrangements  made  by  which  the  materials 
could  be  delivered  through  chutes  down  the  manhole  to  the 
cars  As  it  was  found  more  convenient  to  work  in  winter, 
special  provision  was  made  for  storing  large  quantities  of  ma- 
terial in  the  shanties.  The  sand  was  piled  around  an  iron  lined, 
wooden  bulkhead,  in  the  center  of  which  was  a  large  stove. 

The  concrete  was  mixed  within  the  tunnel  as  close  to  the 
work  as  possible,  and  in  places  where  the  cross-section  had 
been  sufficiently  enlarged  by  falls  of  rock  to  permit  easy  work- 
ing. The  materials,  delivered  to  the  material  cars  down  the 
chutes  already  mentioned,  were  pushed  to  the  mixing  platforms 
and  combined  in  the  proportions  of  18.56  cubic  feet  of  crushed 
stone  and  7.35  cubic  feet  of  sand  to  one  barrel  of  Portland 
cement,  being  approximately  1  to  2  to  5J.  The  above  quanti- 
ties of  materials  made  20  to  21  cubic  feet  of  concrete.  When 
mixed,  the  concrete  was  shoveled  into  cars,  conveyed  to  the 
work  and  then  shoveled  into  place. 

The  tamping  was  done  principally  with  oak  rammer  five 
inches  square,  twelve  inches  long,  with  a  short  wooden  handle 
in  one  end.  In  tamping  the  key  of  the  arch,  long-handled  iron 
rammers  were  used.  Much  care  was  requisite  here  to  prevent 
the  aggregate  separating  from  the  mortar  and  lodging  next 
the  lagging,  as  it  always  has  a  tendency  to  do,  thus  resulting 
in  voids  in  the  face  of  the  work  when  the  lagging  is  removed. 
The  concrete  was  built  up  on  the  sides  in  horizontal  layers  and 
stepped  back  by  inserting  bulkheads,  so  that  the  adjacent 
sections  bonded  together. 

696.  Cost.  —  The  cost  of  this  concrete  lining,  which  was 
built  under  great  disadvantages,  amounted  to  $16.15  per  cubic 
yard.  This  cost  must  be  considered  reasonable  in  view  of  the 
fact  that  the  materials  had  to  be  transported  an  average  dis- 
tance of  more  than  one-half  mile  on  small  push  cars,  and  the 
work  in  the  tunnel  was  suspended  for  three  days  of  each  week 
to  allow  the  tunnel  to  be  used  to  maintain  the  water  supply  of 
the  city. 


RESERVOIRS  453 

ART.  80.     RESERVOIRS:  LININGS  AND  ROOFS 

697.  Although   the   choice   of    the   material   with   which   to 
construct  a   reservoir   may  in  some   cases   be   varied   by  local 
conditions,  it  is  found  that  under  ordinary  circumstances  con- 
crete offers  the  greatest  advantages  for  a  minimum  cost.     For 
the  side  walls  of  small  reservoirs,  concrete  furnishes  the  requi- 
site strength   and   water-tightness  with  a  moderate   thickness; 
earthen  embankments  and  floors  may  be  made  practically  im- 
pervious   with    concrete    and    mortar,    combined    with    asphalt 
when  considered  necessary;  while  for  the  roofs,  groined  arches 
or  beams  and  slab  construction,  with  supporting  piers,  all  of 
this  material,   make  a  neat,   permanent,   and  altogether  satis- 
factory covering,  at  a  smaller  expense  than  would  be  required 
for  brick  or  stone  masonry. 

698.  Details    of     Construction.  —  In    the    walls    and    floors, 
water-tightness  is  a  prime  consideration,   and   this  is  best  at- 
tained by  a  layer  of  mortar  on  the  inner  surfaces  or  between 
two  layers  of  concrete. 

As  in  floors,  walks,  etc.,  the  necessity  of  providing  for  ex- 
pansion and  contraction  will  depend  upon  the  extremes  of 
temperature  to  which  the  surface  is  to  be  subjected.  In  covered 
reservoirs  which  are  to  be  almost  constantly  filled  with  water, 
or  in  very  equable  climates,  the  blocks  may  be  large,  say  twenty 
feet  square,  while  under  more  severe  conditions  the  blocks 
may  not  contain  more  than  twenty  square  feet.  The  joints 
between  the  blocks  may  well  be  wide  enough  to  be  filled  with 
asphalt.  This  furnishes  an  elastic  joint  which  is  compressed 
as  the  blocks  expand,  and  swells  when  the  blocks  again  con- 
tract. 

699.  Reservoir  Floors.  —  One  of  the  principal  difficulties  ex- 
perienced in  the  construction  of  floors  is  from  settlement  of  the 
foundation.     The  floor  should,  therefore,  have  strength  enough 
to  bridge  any  small  irregularities  in  the  foundation  that  may 
result  from  inequalities  in  settlement.     For  a  similar  reason,  it 
is  not  well  to  make  the  blocks  too  large,  as  smaller  blocks  with 
compressible   joints   will   more   readily   conform   to   an   uneven 
surface   without  permanent  injury.     In   order  that  the   reser- 
voir shall  not  leak  even  if  the  foundation  settles,  the  concrete 
and  mortar  may  be  covered  with  one  or  more  layers  of  asphalt. 


454  CEMENT  AND  CONCRETE 

In  building  the  floor  lining,  alternate  blocks  are  sometimes 
placed  first  in  molds  and  the  intermediate  blocks  built  in  later. 
In  other  cases  the  blocks  are  laid  consecutively.  The  advan- 
tage of  the  former  method  seems  to  lie  principally  in  the  ease 
of  construction,  as  access  may  be  had  to  all  sides  of  the 
block. 

700.  In   hard  clay  soil  not  liable  to  settlement,  four  inches 
is  sufficient  thickness  for  the  floor,  the  concrete  to  be  covered 
before  it  has  set  with  a  half-inch  layer  of  rich  Portland  mortar, 
troweled  to  a  smooth  surface.     If  the  reservoir  when  empty 
will   be   subjected   to   hydrostatic   pressure   from   without,   the 
floor  must  be  designed  to  resist  this  pressure.     In  this  case,  if 
seepage  from  without  into  the  reservoir  is  objectionable,  a  layer 
of  mortar  may  be  placed  over  the  first  layer  of  concrete  and 
protected  by  the  concrete  laid  upon  it.     This  outside  pressure 
may  be  provided  for  in  a  covered  reservoir  by  making  the  floor 
of  inverted  arches  between  piers,  the  weight  of  the  floor,  piers, 
roof,  and  earth  filling  over  the  roof,  being  made  sufficient  to 
balance  the  upward  pressure  on  the  floor.     If  there  is  no  ob- 
jection to  the  water  from  without  being  led  into  the  reservoir, 
a  porous  layer  of  broken  stone  or  gravel  beneath  the  floor  may 
be  connected  with  the  interior  of  the  reservoir  through  pipes 
provided  with  check  valves,  and  the  outside  pressure  be  thus 
removed.      Where  it  can   be   accomplished,  it   will  usually   be 
better  to  lead  this  ground  water  through  a  pipe  to  a  sewer  or 
a  lower  level  rather  than  into  the  reservoir. 

701.  Walls.  —  The   thickness  of   the  wall  is  determined  by 
methods  similar  to  those  used  in  designing  a  retaining  wall  or 
a  dam  according  as  the  pressures  are  greater  from  the  embank- 
ment without  or  the  water  pressure  within.     In  the  case  of  a 
covered  reservoir,  the  thrust  of  the  roof  arches  may  convert 
any  vertical  section  of  the  wall  into  a  beam,  the  earth  pressure 
from  without  being  supported  by  the  floor  at  the  bottom  and 
the  roof  at  the  top.     Or  in  case  there  is  no  back  pressure  from 
earth  filling,  the  thrust  of  the  roof  may  be  added  to  the  inner 
water  pressure.     In  circular  covered  reservoirs  the  arch  thrust 
is  usually  taken  by  steel  bands  laid  in  the  concrete  and  en- 
circling the  reservoir  near  the  top   of    the   wall.     In   narrow 
reservoirs  rectangular  in   plan,  tie  rods  may  be  used,  or  the 
wall  may  be  buttressed  to  take  the  roof  thrust.     Concrete  side 


RESERVOIRS  455 

walls  are  usually  built  vertical,  or  nearly  so,  on  the  inside,  and 
with  a  batter  on  the  outside. 

702.  Linings.  —  Linings  of  sloping  earthen  embankments  are 
laid  the  same  as  the  floors,  and  similar  precautions  are  required. 
There  is  greater  danger  of  settlement  of  embankments  than  of 
the  floor  foundation,  and  the  blocks,  therefore,  may  well  be  made 
smaller.     Some  difficulty  may  be  experienced  with  laying  hori- 
zontal asphalt  joints  on  a  sloping  face,  and  some  sliding  of  the 
lining  may  be  expected  under  ordinary  conditions,  the  asphalt 
joints  being  compressed.     For  this  reason  it  would  seem  to  be 
better  to  use  asphalt  in  the  inclined  joints  only,  and  a  mastic 
in  the  horizontal  joints.     Another  method  which  would  probably 
prove  satisfactory  is  to  lay  first  a  tier  of  blocks  next  the  floor, 
and  when  these  have  set,  apply  a  very  thin  coat  of  asphalt  to 
the  upper  edges  of  these  blocks,  following  with  another  tier, 
and  so  on. 

703.  ROOFS.  —  Where  it  is  necessary  to  cover  a  reservoir, 
either  to  prevent  the  formation  of  ice,  or  the  growth  of  algse, 
or  for  other  reasons,  the  groined  arch  is  an  excellent  design  for 
the  roof  on  account  of  the  small  amount  of  concrete  required, 
the  clear  head  room  given,  and  the  ease  of  ventilation.     The 
extending  use  of  reinforced  concrete  will  also  probably  enter 
this  field  to  a  greater  extent  in  the  future  than  it  has  here- 
tofore. 

The  determination  of  the  stresses  in  a  groined  arch  roof  is 
complicated  not  only  by  the  peculiar  form  of  the  arch  itself, 
but  by  the  fact  that  the  spandrels  of  the  arches  are  filled  with 
concrete  over  the  piers  to  the  level  of  the  extrados  at  the  crown. 
This  evidently  results  in  making  of  any  given  unit  of  the  roof, 
having  a  pier  as  its  center,  a  cantilever,  and  the  arch  action  is 
interfered  with.  Unless,  however,  tension  members  of  steel  are 
laid  in  the  concrete  near  its  upper  surface,  it  is  not  wise  to  count 
on  the  strength  of  the  cantilever  except  to  consider  it  a  factor 
of  ignorance  on  the  safe  side.  If  one  wishes  to  depart  from 
the  ordinary  and  tried  dimensions  for  groined  arches  in  concrete, 
such  departure  had  better  be  based  on  some  special  experi- 
ments and  tests  on  full  sized  sections.  Some  of  the  dimensions 
that  have  been  used  are  given  in  the  examples  cited  below. 

704.  Forms.  —  The    preparation    of     forms    or    centers    for 
groined  arches  is  one  of  the  most  difficult  and  expensive  details 


456  CEMENT  AND  CONCRETE 

of  the  construction  of  such  a  roof.  It  will  probably  be  best  to 
have  each  section  of  the  form  cover  the  space,  square  in  plan, 
between  four  piers.  The  ribs  of  the  centering  may  well  be 
built  up  of  planks,  nailed  together  and  sawed  to  proper  form. 
The  lagging  should  be  planed  to  size,  and  have  radial  joints  to 
make  a  smooth  and  even  top  surface.  Care  is  necessary  to  make 
a  neat  fit  along  the  valley  extending  diagonally  between  piers, 
and  a  small  fillet  may  well  be  fitted  into  this  valley  to  avoid 
a  sharp  corner  on  the  finished  concrete,  as  well  as  to  cover  up 
possible  imperfections  in  the  joints.  The  forms  should,  of 
course,  be  designed  to  take  the  thrust  of  the  adjacent  com- 
pleted arches,  and  if  sufficient  forms  are  not  built  to  cover  the 
entire  reservoir,  and  thus  transmit  the  thrust  to  the  walls,  the 
piers  at  the  border  of  the  forms  must  be  thoroughly  braced  to 
the  opposite  side  walls  or  the  piers  will  be  toppled  over  and 
the  roof  wrecked.  This  accident  occurred  to  one  reservoir 
roof  during  construction,  the  pier  braces  having  been  removed 
without  the  knowledge  of  the  engineer. 

705.  In  laying  the  concrete,  joints  between  the  work  done 
on  consecutive  days  should  cut  the  arches  at  right  angles  to 
their  axes,  and  bulkheads  should  be  used  to  make  such  a  joint 
a  vertical  plane.     The  covering  of  each  unit  between  four  piers 
is  made  monolithic,  and  care  is  necessary  to  prevent  the  stones 
working  to  the  bottom  of  the  mass  and  thus  becoming  exposed 
when  the  forms  are  removed.     This  may  be  prevented  by  plas- 
tering the  forms  with  mortar  and  placing  the  concrete  upon  it 
before  the  mortar  has  begun  to  set. 

706.  A  roof  consisting  of  a  network  of  concrete-steel  beams 
intersecting  at  right  angles,  supported  by  piers  and  covered  by 
concrete-steel  slabs,   makes  a  very  simple  design.     The  forms 
are  much  easier  to  construct,  and  forms  for  only  a  limited  area 
need  be  erected  at  one  time.     An  excellent  article  on  "  Covered 
Reservoirs  and  Their  Design,"  by  Mr.  Freeman  C.  Coffin,  M. 
Am.  Soc.  C.  E.,  is  contained  in  the  July,  1899,  number  of  the 
Jour,  of   the  Assn.  of   Engr.  Soc.      An  article  on  the  "  Groined 
Arch,"  by  Mr.  Leonard  Metcalf,  Assoc.  M.  Am.  Soc.  C.  E.,  ap- 
pears in   Trans.  A.    S.  C.  E.  for    June,   1900;  and    Mr.   Frank 
L.  Fuller  presents  an  article  on  "  Covered  Reservoirs,"  in  Jour. 
Assn.  Engr.  Soc.  for  Sept.,  1899. 

707.  Examples    of    Concrete    Reservoirs.      Wellesley.  —  The 


RESERVOIRS  457 

reservoir  at  Wellesley,  Mass.,1  a  part  of  the  water  supply  sys- 
tem, was  designed  by  Mr.  Freeman  C.  Coffin.  It  is  eighty-two 
feet  in  diameter,  walls  fifteen  feet  high,  four  feet  thick  at  bottom 
and  two  feet  at  top.  The  walls  are  of  concrete  and  rubble 
masonry.  In  the  construction  of  the  walls,  concrete  was  used 
containing  three  parts  sand  and  five  parts  of  stone  to  one 
of  cement,  one  cubic  yard  of  concrete  containing  about  1.2 
barrels  of  cement.  The  bottom  of  the  walls,  which  were  de- 
signed to  be  built  of  concrete  three  feet  four  inches  thick,  were 
actually  built  of  rubble  four  feet  thick,  as  a  large  quantity  of 
bowlders  was  at  hand.  The  excavation  was  in  hard  clay  con- 
taining but  little  water,  and  the  floor  was  made  only  four  inches 
thick,  of  concrete  of  the  same  quality  as  that  used  in  the 
walls. 

The  floor  and  side  walls  were  plastered  with  two  coats,  the 
first,  one-half  inch  thick,  of  mortar  containing  two  parts  sand 
to  one  of  Portland  cement,  and  a  coat  about  one-eighth  inch 
thick,  of  neat  Portland  carefully  rubbed  and  smoothed  with 
trowels.  Such  a  plaster  coat  should  be  applied  before  the  con- 
crete has  set.  The  two  plaster  coats  cost  twenty  cents  per 
square  yard. 

708.  The  piers  to  support  the  groined  arch  roof  were  two 
feet  square,  and  built  of  brick.  The  span  of  the  arches  was 
12  feet,  rise  2.5  feet,  and  the  concrete  0.5  foot  thick  at  the 
crown.  A  channel  iron  ring  or  band  was  set  in  the  concrete 
walls  at  the  springing  of  the  roof  arches  to  take  the  thrust  of 
the  latter.  The  centers  were  placed  over  one-fourth  of  the 
area  at  a  time,  the  piers  being  braced  to  take  the  thrust  of  the 
arches  until  the  roof  was  completed.  The  concrete  in  the  roof 
was  composed  of  two  and  one-half  parts  sand  and  four  and  one- 
half  parts  broken  stone  to  one  part  Portland  cement.  The 
centering  cost  twenty-two  and  one-half  cents  per  square  foot  of 
area  covered.  The  spandrels  were  filled  in  level  with  top  of 
concrete  at  crown.  On  top  of  the  concrete  roof  was  placed  six 
inches  of  clean  gravel  for  drainage  and  to  prevent  the  earth 
freezing  to  the  concrete.  This  gravel  was  drained  by  four 
inch  vitrified  pipe  discharging  at  the  toe  of  the  slope  wall. 


1  Engineering  News,  Sept.  30,   1897;  Jour.  Assn.  Engr.  Societies,  July 
1899;  Trans.  A.  S.  C.  E.,  June,  1900. 


458  CEMENT  AND  CONCRETE 

One  foot  of  earth  filling  and  one  foot  of  loam  were  placed  upon 
the  gravel. 

709.  Astoria.  —  The  reservoir  for  the    Astoria  City  Water 
Works  *  was  designed  and  built  by  Mr.  Arthur  L.  Adams,  M. 
Am.  Soc.  C.  E.     The  reservoir  has  a  capacity  of  six  and  one- 
fourth  million  gallons,  walls  twenty  feet  high.     The  excavation 
was  in  hard  clay  and  sand  mixed  with  clay,  which  in  some  places 
resembled  a  soft  sandstone.     The  embankment  was  in  general 
about  five  feet,  the  remainder  of  the  depth  being  in  excavation. 

The  floor  consisted  of  six  inches  of  concrete,  f  inch  cement 
mortar,  one  coat  liquid  asphalt  and  one  coat  harder  asphalt. 
The  slope  lining  was  of  six  inches  concrete,  one  coat  asphalt, 
one  layer  of  brick  dipped  in  asphalt  and  laid  flat,  and  a  final 
finishing  coat  of  asphalt.  The  concrete  was  composed  of  one 
barrel  Portland  cement,  one-tenth  cubic  yard  sand,  five-tenths 
cubic  yard  gravel  and  nine-tenths  cubic  yard  of  crushed  stone, 
these  quantities  of  the  ingredients  making  one  cubic  yard  of 
concrete.  Here  we  have  an  instance  of  the  use  of  a  mixture 
of  broken  stone  and  gravel,  a  practice  which  has  already  been 
commended  as  resulting  in  a  small  amount  of  voids. 

The  concrete  of  the  floor  was  laid  in  blocks  twenty  feet  on  a 
side,  molds  of  two  by  six  inch  plank  forming  the  outside  edges 
of  a  block,  and  serving  as  a  guide  to  the  straight  edge  used  in 
finishing,  as  in  concrete  walk  construction.  The  finishing  coat 
was  of  two  parts  fine  sand  to  one  of  Portland  cement  and  was 
applied,  before  the  concrete  base  had  begun  to  set,  by  two 
finishers  with  smoothing  trowels.  When  the  next  block  was  to 
be  laid,  the  plank  were  replaced  by  one-half  inch  weather 
boarding.  When  the  concrete  had  thoroughly  set,  these  boards 
were  removed  and  the  joints  so  formed  were  run  full  of  asphalt, 
when  the  first  layer  of  this  material  was  spread. 

The  concrete  on  the  sides  was  also  six  inches  thick  and  laid 
in  sheets  ten  feet  wide,  extending  up  and  down  the  slopes, 
expansion  joints  being  provided  on  the  inclined  joints  only. 
The  finishing  coat  of  mortar  was  not  used  here,  but  all  inequali- 
ties in  surface  were  smoothed  by  using  a  little  mortar  from  the 
next  batch  of  concrete. 

710.  Each  concrete  gang  was  composed  of  twenty  men  and 


1  Trans.  A.  S.  C.  E.,  December,  1896. 


RESERVOIRS  459 

one  water  boy.  All  concrete  was  mixed  by  hand  on  movable 
platform  in  half-yard  batches.  On  the  entire  work  1.84  cubic 
yards  of  concrete  per  day  were  mixed  and  placed  per  man 
employed,  and  on  the  floor  alone  this  quantity  was  increased 
to  2.oo  cubic  yards,  an  excellent  showing  for  this  class  of  work. 
The  cost  of  concrete  per  cubic  yard,  without  profit,  was  as 
follows:  — 

On  Slopes:— Cement,  at  $2.45  per  bbl $2.82 

Other  materials 1.94 

Labor 1.07 

Total  per  cubic  yard  for  600  yards $5.83 

On  Floor: —Cement,  at  $2.45 $2.64 

Other  materials 1.92 

Labor .68 


Total  cost  per  cubic  yard  for  680  yards $5.24 

The  costs  of  the  slope  lining  and  floor  complete,  per  square  foot, 
are  given  as  follows:  - 

Slope: — 6  inches  concrete $0.1187 

.649  inch  asphalt 0100 

Brick  in  asphalt 0889 

.851  inch  asphalt 0131 

Chinking  crevices 0030 

Ironing 0036 

Total  cost  per  square  foot  of  slope $0.2373 

Bottom :— 6  inches  concrete $0.1031 

Cement  mortar  finish 0113 

.537  inch  coat  asphalt 0077 

.573  inch  coat  asphalt 0082 

Total  cost  of  bottom  per  square  foot $0.1303 

711.  Forbes  Hill.  —  The  Forbes  Hill  reservoir  *  forms  a  part 
of  the  distribution  system  of  the  Metropolitan  Water  Works  of 
Boston  and  was  built  under  the  direction  of  Mr.  Dexter  Brack- 
ett,  M.  Am.  Soc.  C.  E.  The  reservoir  is  two  hundred  eighty  by 
one  hundred  feet,  partly  in  embankment.  The  soil  under  the 
embankment  was  first  stripped  to  a  depth  of  two  and  one-half 


1  Described  by  Mr.  C.  M.  Saville,  M.  Am.  Soc.  C.  E.,  Division  Engineer, 
before  the  N.  E.  Water  Works  Assn.  Abstracted  in  Engineering  News,  March 
13,  1902. 


460  CEMENT  AND  CONCRETE 

feet  at  the  toe,  increasing  to  five  feet  stripping  at  the  inner  edge 
of  the  slope.  The  material  was  hard  pan,  and  the  embank- 
ments were  built  in  four  inch  layers,  rolled  with  four  thousand 
pound  rollers,  so  made  as  to  leave  a  slightly  corrugated  surface. 
The  bank  was  extended  one  foot  inside  of  the  finished  line  to 
assure  a  compact  face,  and  afterward  trimmed  to  grade. 

712.  The  bottom  of    the  reservoir  was  covered  first  with  a 
layer  of  concrete  about  four  and  one-half  inches  thick,   com- 
posed of  one  part  natural  cement,   two   parts  sand,   and   five 
parts  stone.     The  sand  was  of  good  quality;  the  stone  came  from 
the  excavation  and  was  washed  before  crushing.     This  layer  of 
natural  cement  concrete  was  covered  by  a  layer  of  Portland 
cement  mortar  one-half  inch  thick,  made  of  two  parts  sand  to 
one  cement,  and  finished  with  a  richer  mortar,  one  part  sand  to 
four  of  cement. 

This  half-inch  layer  was  laid  in  strips  four  feet  wide  and 
finished  like  a  cement  sidewalk.  Although  this  mortar  coat 
was  kept  well  moistened,  some  cracks  developed  which  were 
filled  with  grout  before  applying  the  second  layer  of  concrete. 
If  no  joints  were  used  in  the  lower  layer  or  base  concrete,  and 
joints  in  the  coat  of  mortar  were  provided  in  one  direction  only, 
as  appears  to  have  been  the  case,  the  cracking  should  have  been 
anticipated.  At  any  rate,  the  value  of  the  mortar  coat  be- 
tween the  two  concrete  layers  was  greatly  impaired  by  this 
cracking,  and  the  experience  points  to  the  advisability  of  plac- 
ing the  upper  layer  of  concrete  on  the  mortar  before  the  latter 
has  set,  thus  avoiding  the  expense  of  finishing  the  mortar  layer. 

The  upper  layer  of  concrete  was  composed  of  one  part  Port- 
land cement,  two  and  one-half  parts  sand  and  four  parts  broken 
stone,  and  was  laid  in  blocks  ten  feet  square.  These  blocks 
were  laid  alternately  each  way. 

The  slope  was  first  lined  with  Portland  concrete  of  1  to  2J 
to  6^,  then  one-half  inch  layer  of  mortar  as  for  the  bottom. 
The  upper  layer  of  concrete  on  slope  was  same  as  the  upper 
layer  of  the  bottom  lining,  but  the  blocks  were  eight  by  ten 
feet  and  finished  with  one  inch  of  granolithic,  in  which  stone 
dust  and  particles  smaller  than  three-eighths  inch  were  sub- 
stituted for  the  one  and  one-half  inch  stone  of  the  concrete. 

713.  Cost.  —  The  cost  of  lower  layer  of  concrete  on  bottom, 
natural  1  to  2  to  5,  was  as  follows :  — 


RESERVOIRS  461 

1.25  bbl.  natural  cement,  at  $1.08 $1.350 

.34  cu.  yd.  sand,  at  $1.02 347 

.86  cu.  yd.  stone,  at  $1.57 1.350 


Materials  in  concrete $3.047 

Forms,  lumber,  at  $20.00  per  M                        ...     $0.090 
Forms,  labor 0.100 


Total  forms .190 

General  expenses $0.08 

Mixing  and  placing 1.17 

1.250 


Total  cost  per  cu.  yd $4.487 

Cost  of  lower  layer  on  slopes,  Portland  1  to  2J  to  6J,  was  as 
follows:  — 

1 . 08  bbls.  Portland  cement,  at  $1.53 $1.652 

.37  cu.  yd.  sand,  at  $1.02 377 

.96  cu.  yd.  stone,  at  $1.57 1.507 


Materials  in  concrete      ..........  $3.536 

Forms,  lumber,  at  $20.00  per  M $0.016 

Forms,  labor 0.121 


Total  forms .137 

General  expenses $0.177 

Mixing  and  placing 1.213 

••       1.390 

Total  cost  per  cubic  yard $5.063 

The  cost  of  the  upper  layer  on  bottom  and  slopes,  including 
the  finish  on  slopes,  Portland  1  to  2£  to  4,  was  as  follows:  - 

1.37  bbls.  Portland  cement,  at  $1.53 $2.09 

.47  cu.  yd.  sand,  at  $1.02 48 

.745  cu.  yd.  stone,  at  $1.57 1.17 

Materials  in  concrete $3.74 

Forms,  lumber,  at  $20.00  per  M $0.25 

Forms,  labor 0.26 

Total  forms .51 

General  expenses • $0.15 

Mixing  and  placing 1.53 

1.68 


Total  cost  per  cu.  yd $5.93 


462  CEMENT  AND  CONCRETE 

The  cost  of  the  half-inch  plaster  coat  between  the  layers  of 
concrete  was  twenty  cents  per  square  yard. 

714.  Rockford.  —  A  reservoir  for  the  city  of  Rockford,  111.,1 
was  built  almost  entirely  of  concrete  after  plans  prepared  by 
the  City  Engineer,  Mr.  Chas.  C.  Stowell.     The  soil  was  a  loose 
gravel,   and  after  excavation   was  completed,   parallel  lines  of 
drain  tile  were  laid  in  trenches  nine  to  ten  feet  centers  and 
leading  to  a  fifteen  inch  vertical  sewer  pipe  carried  to  the  sur- 
face of  the  street  and  capped.     This  sewer  pipe  served  as  a 
sump  for  a  pump  should  it  be  found  necessary  at  any  time  to 
repair  the  bottom.     These  trenches  were  filled  with  broken  stone 
and  the  whole  area  of  the  foundation  covered  with  three  inches 
of  clay.     The  concrete  bottom  was  in  two  layers,  eight  inches 
and   seven   inches   thick,   respectively,    and   composed   of   two 
parts  sand  and  five  parts  stone  to  one  of  Portland  cement. 

The  walls  were  of  similar  concrete  for  the  bottom  twelve  feet, 
natural  cement  being  used  in  the  upper  eight  feet  of  the  walls. 
The  thickness  at  the  bottom  was  4^  feet,  walls  being  straight  on 
outside  with  one  to  ten  batter  on  inside.  The  entire  inner 
surface  of  floor  and  walls  was  plastered  with  one-half  inch  of 
Portland  mortar,  one  to  one.  The  cost  of  concrete  in  the  work 
averaged  $6.50  for  Portland  and  $4.00  for  natural,  and  the 
finishing  coat  cost  seventy-five  cents  a  square  yard. 

715.  The  roof  was  of    concrete,  expanded  metal  lath,  and 
steel  rods,  the  finished  thickness  being  but  two  inches.     This 
was  supported  by  ribs  of  concrete,  each  twelve  inches  thick  at 
the  crown  and  having  a  seven-inch  channel  on  the  under  side. 
The  springing  line  of  the  ribs  was  eight  feet  below  the  top  of 
the  walls,  giving  a  good  depth  at  the  skew  back.     Ribs  were 
spaced  about  seven  feet  centers.     The  span  of  the  roof  was 
about  fifty-five  feet,  and  rise  about  eleven  feet.     The  cost  of 
roof  was  less  than  twenty-five  cents  a  square  foot. 

716.  Concord.  —  The    groined    arch    roof    of    the    Concord, 
Mass.,1  sewage  storage  well,  designed  by  Mr.  Leonard  Metcalf, 
Assoc.  M.  Am.  Soc.  C.  E.,  was  fifty-seven  feet  diameter  and 
contained  about  one  hundred  cubic  yards  of  masonry.     The 
cost  of  the  roof  per  square  foot  of  surface  was  as  follows:  — 


Described  in  Engineering  News,  Feb.  22,  1894. 


RESERVOIRS  463 

Centering $0.18 

Concrete  materials .15 

Labor  and  supervision      .05 

Total $0.38 

717.  Albany.  —  The  Albany  filter  plant  roof,1  designed  by 
Mr.  Allen  Hazen,  Assoc.  M.  Am.  Soc.  C.  E.,  was  also  of  the 
groined  arch  type,  the  arches  having  the  same  span  and  rise  as 
the  Wellesley  reservoir.  The  cost  of  the  roof  per  square  foot 
of  area  was  as  follows:  - 

.029  cu.  yd.  concrete,  at  $6.30 $0.182 

Piers 054 

Earth  filling  and  seeding 014 

Manholes,  entrances,  etc .027 


Total  cost  per  sq.  ft $0.277 

For  a  list  of  reservoirs  and  filter  beds,  in  the  roofs  of  which 
groined  arches  have  been  used,  giving  in  tabular  form  the 
general  dimensions,  the  proportions  used  in  the  concrete,  and 
in  several  cases  the  cost  of  the  roof  per  square  foot  of  reservoir, 
the  reader  is  referred  to  Engineering  News  of  December  24, 
1903. 


Trans.  A.  S.  C.  E.,  June,  1900. 


CHAPTER  XXII 

SPECIAL  USES  OF  CONCRETE  (CONTINUED) 
BRIDGES,  DAMS,   LOCKS,   AND   BREAKWATERS 

ART.  81.     BRIDGE  PIERS  AND  ABUTMENTS  AND  RETAINING 

WALLS 

718.  The  use  of  concrete  in  large  bridge  piers  was  at  first 
confined  to  the  hearting  or  backing  of  stone  masonry  shells. 
It  was  soon  found,  however,  that  in  many  cases  the  concrete 
was  able  to  withstand  the  effects  of  frost  and  ice  better  than 
was  the  variety  of  stone  available  for  building  the  masonry 
shell,  and  many  important  bridges  are  now  supported  by  piers 
built  entirely  of  concrete. 

As  an  example  of  this  use  may  be  mentioned  the  bridge 
across  the  Red  River  *  in  Louisiana,  which  has  six  concrete 
piers  of  heights  from  forty-four  to  fifty-three  feet.  The  pivot 
pier  is  twenty-seven  feet  in  diameter,  with  vertical  sides.  The 
draw  rest  piers  are  seven  feet  wide  under  the  coping,  nineteen 
feet  between  shoulders  and  twenty-six  feet  long  over  all.  The 
sides  have  a  batter  of  one-half  inch  to  the  foot.  The  coping  is 
of  limestone. 

719.  In  the  construction  of  the  Arkansas  River  Bridge  2  of 
the  K.  C.  P.  &  G.  R.  R.,  ten    piers    and  two  abutments    were 
built  of  concrete.     The  piers  varied  in  height  from  twenty  to 
sixty-five  feet,  some  of  them  containing  over  six  hundred  cubic 
yards  of  concrete.     The  entire  work  was  completed  in  eleven 
months,   although   many   difficulties   were   met.     The   concrete 
was  composed  of  one  part  Portland  cement,  two  and  one-half 
parts  coarse,  sharp  sand,  and  five  parts  of  clean,  broken  stone. 

The  lagging  for  the  forms  was  of  two-inch  yellow  pine,  sur- 
faced one  side  and  sized  to  one  and  three-quarters  inches.  On 


1  George  H.  Pegram,  Consulting  Engineer.    Walter  H.  Gahagan,  Engi- 
neer for  Contractors. 

2  Engineering  News,  Aug.  25,  1898. 

464 


BRIDGE  PIERS  465 

the  straight  part  of  the  pier  this  lagging  was  laid  horizontal  and 
supported  by  four  by  six  vertical  posts  set  four-feet  centers, 
posts  on  opposite  sides  of  the  pier  being  tied  together  by  three- 
quarter  inch  bolts  passing  through  one  and  one-half  inch  gas 
pipes  spaced  five  feet  vertically.  The  gas  pipe  was  allowed  to 
remain  in  the  finished  pier,  the  bolts  being  withdrawn. 

The  lagging  for  the  semicircular  ends  was  of  two  by  six  with 
bevel  joints,  placed  vertical,  and  supported  at  five-foot  inter- 
vals by  segmental  ribs  of  double  two  by  twelve  planks.  At 
the  ends  of  the  ribs  were  bolted  short  pieces  of  eight  by  eight 
inch  angle  irons  with  edge  horizontal.  These  angle  irons  were, 
in  turn,  bolted  to  four  by  six  verticals  at  the  corners  or  shoul- 
ders of  the  pier. 

720.  The  foundation  piers  of  the  Lonesome  Valley  Viaduct,1 
thirty-six  piers  and  two  abutments,   are  entirely  of  concrete. 
The  piers  are  four  feet  square  on  top  with  batter  of  one  inch 
to  the  foot,  and  are  from  five  to  sixteen  feet  in  height.     The 
total  concrete  laid  was  926  cubic  yards  at  a  contract  price  of 
about  $7.00  per  cubic  yard.     The  piers  were  finished  on  top  with 
a  steel  plate,  four  feet  square  and  one-half  inch  thick,  taking 
the  place  of  coping  stones.     Where  rock  foundations  were  not 
found,   the  lower  portion  of  the  pier  was  given  an  increased 
batter  to  secure  such  a  cross-sectional  area  at  the  bottom  that 
the  unit  pressure  on  the  earth  did  not  exceed  one  ton  per  square 
foot.     The  cost  of  the  concrete  for  this  work  has  already  been 
given  (§  322). 

721.  Steel  Cylinders.  —  Steel  shells  filled   with  concrete  have 
been  used  to  good  advantage,  especially  for  bridge  approaches. 
Such  shells  are  usually  in  pairs  placed  abreast,  one  under  each 
truss  of  the  bridge  or  viaduct.     The  two  cylinders  of  a  pair 
are  usually  connected  by  lateral  bracing,  and  if  desired  in  heavy 
work,  this  bracing  may  be  inclosed  in  a  concrete  wall  and  thus 
protected  from  injury  by  running  ice,  etc.     The  thickness  of 
metal  in  the  shells  need  not  be  great,  three-eighths  of  an  inch 
usually  being  sufficient,  though  this  depends  on  the  height,  the 
stresses,  and  the  liability  to  injury.     In  soft  ground  requiring 
piles,  most  of  the  piles  are  sawn  off  below  the  limit  of  scour,  or 
below  the  water  line  for  land  piers,  but  one  or  more  may  be 


Gustave  R.  Tuska,  Trans.  A.  S.  C.  E.,  September,  1895. 


466  CEMENT  AND  CONCRETE 

allowed  to  project  up  into  the  cylinders  and  the  concrete  filled 
in  around  the  heads,  thus  anchoring  the  pier.  In  foundations 
on  rock  if  the  cylinders  require  an  anchorage,  this  may  be  pro- 
vided with  bolts  fox-wedged  or  cemented  in  the  rock  and  pro- 
jecting into  the  cylinder.  (For  details  of  methods  adopted  in 
this  class  of  construction,  see  "  Bridge  Substructure  and  Foun- 
dations in  Nova  Scotia/'  by  Martin  Murphy,  Trans.  A.  S.  C.  E., 
September,  1893.) 

722.  Repair  of  Stone  Piers.  —  Where  masonry  piers  are  being 
destroyed  by  the  abrading  or  expansive  action  of  ice,  or  by 
other  causes,  concrete  is  successfully  used  to  arrest  such  action, 
the  entire  pier  being  incased  in  a  layer,  one  to  three  feet 
thick,  of  Portland  cement  concrete  of  good  quality. 

The  piers  of  the  Avon  River  bridge,1  originally  built  of  ashlar 
masonry,  failed  entirely  to  withstand  the  deteriorating  in- 
fluences of  an  extreme  range  in  tide  coupled  with  the  severe 
temperature  of  a  Nova  Scotia  winter.  Five  of  them  were  sub- 
sequently incased  in  concrete,  as  follows:  A  form  was  made  of 
ten  by  ten  inch  spruce  timber  surrounding  the  ashlar  masonry 
of  the  piers  and  forming  a  mold  to  receive  the  concrete  and 
retain  it  in  place  until  set.  The  thickness  of  the  concrete  casing 
was  two  and  one-half  feet  at  the  bottom  and  one  and  one- 
third  feet  at  the  top,  which  was  three  feet  above  high  water. 
The  concrete  was  composed  of  one  barrel  Portland  cement, 
one  and  one-half  barrels  clean  sand,  one  barrel  of  clean  gravel, 
and  in  it  was  placed  by  hand  four  parts  of  common  field  stone 
weighing  from  eight  to  twenty  pounds  each.  This  treatment 
was  entirely  successful  in  preventing  further  disintegration. 

723.  An  efficient  cutwater  for  bridge  piers  is  made  by  placing 
old  rails  vertically  on  the  upstream  nose  of  the  pier,  anchoring 
them  to  the  masonry  and  filling  between  with  concrete,  leaving 
only  the  wearing  surface  of  the*rail  head  exposed. 

724.  Pneumatic  caissons  are  usually  filled  with  concrete,  the 
filling  over  the  working  chamber  being  carried  up  fast  enough 
to  keep  the  work  above  water  as  the  caisson  is  sunk.     The 
filling  of  the  working  chamber  calls  for  special  care  in  tamping 
under  and  around  the  longitudinal  and  cross-timber  braces.     A 
space  of  about  three  inches  next  the  roof  of  the  chamber  is 


1  Trans.  A.  S.  C.  E.,  December,  1893. 


RETAINING  WALLS  AND  ABUTMENTS  467 

filled  with  a  rich  concrete,  containing  no  stone  larger  than  one 
inch,  mixed  quite  dry  and  solidly  tamped  with  special  edge 

rammers. 

725.  RETAINING  WALLS  AND  ABUTMENTS.  —  Concrete  is  used 

very  largely  for  constructing  retaining  walls  and  bridge  abut- 
ments. The  foundations  of  a  retaining  wall  should  be  of  ample 
width,  and  if  the  wall  is  not  founded  on  rock,  some  settlement 
and  outward  movement  may  be  expected  if  the  common  for- 
mulas are  used  in  computing  the  dimensions. 

If  this  movement  is  not  equal  throughout  the  wall,  cracking 
is  likely  to  take  place,  and  to  confine  these  cracks  to  prede- 
termined vertical  planes,  it  is  well  to  construct  the  wall,  if  a 
long  one,  with  vertical  joints  at  intervals  of  fifteen  to  thirty 
feet.  Such  a  joint  is  made  by  building  one  section  and  fol- 
lowing with  another,  without  special  precautions  to  make  a  bond 
between. 

If  there  is  an  opportunity  for  water  to  accumulate,  care 
should  be  taken  to  drain  the  earth  back  of  the  wall,  either  by 
drains  leading  around  the  ends,  or  by  pipes  passing  through 
the  wall.  The  latter  may  result  in  discoloration  of  the  face. 

726.  Coping.  —  The  face  of  a  retaining  wall  or  abutment  is 
preferably  given  a  batter,  and  a  coping  is  provided  to  improve 
the  appearance.     The  coping  should  have  a  slight  inclination 
toward  the  back  to  prevent  the  discoloration  of  the  face  by 
dripping.     It  should  be  divided  by  vertical  joints  into  blocks, 
not  more  than  six  to  eight  feet  in  length.     The  projection  of 
the  coping  will  depend  upon  the  dimensions  of  the  wall.     Wing 
walls  are  preferably  built  with  a  sloping  top  or  coping,  but  this 
should   be    made    monolithic  with  the  wall  by   special   molds 
(§729). 

727.  Rules  for  Use  of  Concrete  in  Abutments.  —  In  the  use 
of  concrete  for  abutments  and  piers,  the  practice  of  the  Illinois 
Central  Railroad,  as  set  forth  in  their  specifications,  can  hardly 
be  improved  upon.     The  engineer  of  bridges  and  buildings  on 
this  road,  Mr.  H.  W.  Parkhurst,  M.  Am.  Soc.  C.  E.,  is  one  of 
those  engineers  who  early  recognized  the  value  of  concrete  in 
bridge  work,  and  as  the  result  of  his  extensive  experience  along 
this  line,  he  is  widely  known  as  an  able  and  conservative  au- 
thority. 

These  specifications  are  printed  nearly  in  full  in  Engineering 


4G8  CEMENT  AND  CONCRETE 

News  of  July  18,  1901,  from  which  the  following  extracts  are 
made:  — 

728,    Natural  and  Portland  Cement :  Where  used  :  - 

Natural  cement  concrete  "may  be  used  where  foundations 
are  entirely  submerged  below  low-water  mark,  or  where  there  is 
no  risk  of  the  same  being  exposed  to  the  action  of  the  weather 
by  cutting  away  the  surrounding  earth.  It,  however,  shall  be 
used  only  where  a  firm  and  uniform  foundation  is  found  to 
exist*  after  excavations  are  completed.  In  all  cases  where 
foundations  are  liable  to  be  exposed  to  the  action  of  the  water, 
or  where  the  material  in  the  bottom  of  excavations  is  soft  or 
of  unequal  firmness,  Portland  cement  concrete  must  be  em- 
ployed for  foundation  work. 

"The  natural  cement  concrete  shall  usually  be  made  in  the 
proportions  (by  measure)  of  one  part  of  approved  cement  to 
two  parts  of  sand  and  five  parts  of  crushed  stone,  all  of  char- 
acter as  above  specified.  For  Portland  cement  concrete  foun- 
dations, one  part  of  approved  cement,  three  parts  of  sand  and 
six  parts  of  crushed  stone  may  be  used.  Wherever  in  the 
judgment  of  the  engineer  or  inspector  in  charge  of  the  work,  a 
stronger  concrete  is  required  than  is  above  specified,  the  pro- 
portions of  sand  and  crushed  stone  employed  may  be  reduced, 
a  natural  cement  concrete  of  1,  2  and  4,  and  a  Portland  cement 
concrete  of  1,  2  and  5  being  substituted  for  those  above  speci- 
fied. 

"Portland  Cement  Concrete:  — Concrete  for  the  bodies  of 
piers  and  abutments,  for  all  wing- walls  for  same,  and  for  the 
bench  walls  of  arch  culverts,  shall  generally  be  made  in  the  pro- 
portions (by  measure)  of  one  part  of  cement,  two  and  one-half 
parts  of  sand  and  six  parts  of  crushed  stone.  Where  special 
strength  may  be  required  for  any  of  this  work,  concrete  in  the 
proportions  of  1,  2  and  5  may  be  used;  but  all  such  cases  shall 
be  submitted  to  the  judgment  of  the  engineer  of  bridges,  before 
any  change  from  the  usual  specification  is  to  be  allowed. 

"For  arch  rings  of  arch  culverts  and  for  parapet  head  walls 
and  copings  to  same,  Portland  cement  concrete,  in  proportions 
of  1,  2  and  5,  shall  generally  be  used.  Concrete  of  these  pro- 
portions shall  also  generally  be  used  for  parapet  walls  behind 
bridge  seats  of  piers  or  abutments,  and  for  the  finished  copings 
(if  used)  on  wing-walls  of  concrete  abutments,  also  for  arch 


USE  OF  CONCRETE  AND  ABVTMENTS  469 

work  in  combination  with  I-beams  or  in  combination  with  iron- 
work for  transverse  loading. 

"  Bridge  seats  of  piers  and  abutments  and  copings  of  con- 
crete masonry  which  are  to  carry  pedestals  for  girders  or  longer 
spans  of  ironwork,  shall  generally  be  made  of  crushed  granite 
and  Portland  cement,  in  the  proportion  (by  measure)  of  one 
part  of  approved  cement,  two  parts  of  fine  granite  screenings, 
and  three  parts  of  coarser  granite  screenings,  the  larger  of  which 
shall  not  exceed  three-quarters  inch  in  greatest  dimension." 

729.  After  specifying  the  method  of  building  molds,  which 
is  treated  elsewhere  (Art.  62),  the  specifications  proceed:  - 

"The  planking  forming  the  lining  of  the  molds  shall  in- 
variably be  fastened  to  the  studding  in  perfectly  horizontal 
lines ;  the  ends  of  these  planks  shall  be  neatly  butted  against 
each  other,  and  the  inner  surface  of  the  mold  shall  be  as  nearly 
as  possible  perfectly  smooth,  without  crevices  or  offsets  be- 
tween the  sides  or  ends  of  adjacent  planks.  Where  planks  are 
used  a  second  time,  they  shall  be  thoroughly  cleaned,  and,  if 
necessary,  the  sides  and  ends  shall  be  freshly  jointed  so  as  to 
make  a  perfectly  smooth  finish  to  the  concrete. 

"The  molds  for  projecting  copings,  bridge  seats,  parapet 
walls,  and  all  finished  work  shall  be  constructed  in  a  first-class 
workmanlike  manner,  and  shall  be  thoroughly  braced  and  tied 
together,  dressed  surfaces  only  being  exposed  to  the  contact  of 
concrete,  and  these  surfaces  shall  be  soaped  or  oiled  if  necessary, 
so  as  to  make  a  smoothly  finished  piece  of  work.  The  top 
surfaces  of  all  bridge  seats,  parapets,  etc.,  shall  be  made  per- 
fectly level,  unless  otherwise  provided  in  the  plans,  and  shall 
be  finished  with  long,  straight  edges,  and  all  beveled  surfaces 
or  washes  shall  be  constructed  in  a  true  and  uniform  manner. 
Special  care  shall  be  taken  in  the  construction  of  the  vertical 
angles  of  the  masonry,  and  where  I-beams  or  other  ironwork 
are  not  used  in  the  same,  small  wooden  strips  shall  be  set  in  the 
corners  of  the  mold,  so  as  to  cut  off  the  corners  at  an  angle  of 
45°,  leaving  a  beveled  face  about  one  and  one-half  to  two  inches 
wide,  instead  of  a  right-angled  corner. 

"Where  wing- walls  are  called  for,  which  have  slopes  corre- 
sponding to  the  angle  of  repose  of  earth  embankments,  these 
slopes  shall  be  finished  in  straight  lines  and  surfaces,  the  mold 
for  such  wing-walls  and  slopes  being  constructed  with  its  top 


470  CEMENT  AND  CONCRETE 

at  the  proper  slope,  so  that  the  concrete  work  on  the  slope  may 
be  finished  in  short  sections,  say  from  three  to  four  feet  in 
length,  and  bonded  into  the  concrete  of  the  horizontal  sections 
before  the  same  shall  be  set,  each  short  section  of  sloped  sur- 
face being  grooved  with  a  cross-line  separating  it  from  adjacent 
sections.  It  will  not  be  permitted  to  finish  the  top  surface  of 
such  sloped  wing-walls  by  plastering  fresh  concrete  upon  the 
top  of  concrete  which  has  already  set,  but  the  finished  work 
must  be  made  each  day  as  the  horizontal  layers  are  carried  up, 
to  accomplish  which  the  mold  must  be  constructed  complete  at 
the  outset;  or,  if  the  wing- wall  is  very  high,  short  sections  of 
the  mold,  including  the  form  for  the  slopes,  must  be  completed 
as  the  horizontal  planking  is  put  in  place." 

730.  This  is  followed  by  directions  concerning  foundation 
work;  the  following  is  given  relative  to  building  steel  into  the 
masonry :  - 

"Iron  rails  to  be  furnished  by  the  railroad  company  shall  be 
laid  and  imbedded  in  such  manner  as  may  be  specified  in  such 
foundation  concrete  as  in  the  opinion  of  the  engineer  of  bridges 
needs  such  strengthening,  and  no  extra  charge,  except  the 
actual  cost  of  handling  the  same,  shall  be  made  by  the  contrac- 
tor for  such  work,  but  the  volume  of  such  iron  shall  be  esti- 
mated as  concrete. 

"Where  I-beams  are  to  be  placed  in  the  angles  of  concrete 
piers  as  a  protection  against  ice,  drift,  etc.,  these  shall  be  set 
up  and  securely  held  in  position  so  that  they  will  extend  one 
foot  or  more  into  the  foundation  concrete.  The  planking  of 
molds  shall  be  fitted  carefully  to  the  projecting  angles  of  these 
I-beams,  and  small  fillets  of  wood  shall  be  fitted  in  between 
the  inner  faces  of  the  mold  and  the  rounded  edges  of  the  I-beam 
flanges,  so  that  no  sharp  projecting  angle  of  concrete  will  be 
formed  as  the  work  is  constructed. 

"These  fillets  may  be  made  in  short  pieces  and  fastened 
neatly  into  the  mold  as  the  layers  of  concrete  are  carried  up. 
Such  I-beams  will  generally  be  furnished  of  sufficient  length  to 
extend  at  least  six  inches  above  the  top  of  the  battered  masonry 
into  the  concrete  coping,  and  special  pains  shall  be  taken  to 
tamp  the  concrete  thoroughly  around  the  I-beams,  and  to 
finish  the  coping  above  and  around  the  ends  of  the  same,  so  as 
to  make  a  compact  and  solid  bearing  against  the  ironwork. 


CONCRETE  PILES  471 

"  Where  anchor  bolts  for  bridge-seat  castings  are  required, 
they  shall  be  set  in  place  and  held  firmly  as  to  position  and 
elevation,  by  templets,  securely  fastened  to  the  mold  and 
framing.  Such  I-beams  and  anchor  bolts  shall  be  imbedded 
in  the* concrete  work  without  additional  expense  beyond  the 
price  to  be  paid  per  yard  for  the  several  classes  of  concrete  in 
which  such  iron  is  placed,  the  volume  of  iron  being  estimated 
as  concrete. 

"After  the  work  is  finished  and  thoroughly  set,  all  molds 
shall  be  removed  by  the  contractor.  They  shall  generally  be 
allowed  to  stand  not  less  than  forty-eight  hours  after  the  last 
concrete  work  shall  have  been  done.  In  cold  weather,  molds 
shall  be  allowed  to  stand  a  longer  period  before  being  removed, 
depending  upon  the  degree  of  cold.  No  molds  shall  be  re- 
moved in  freezing  weather,  nor  until  after  the  concrete  shall 
have  had  at  least  forty-eight  hours,  with  the  thermometer  at 
or  above  40°  Fahr..  in  which  to  set.'' 

731.  After  giving  in  detail  the  methods  to  be   followed  in 
placing  and  ramming  concrete  and  the  use  of  facing  mortar, 
the  following  paragraph  is  especially  applicable  to  the  subject 
in  hand: 

"  Layers  of  concrete  shall  be  kept  truly  horizontal,  and  if, 
for  any  reason,  it  is  necessary  to  stop  work  for  an  indefinite 
period,  it  shall  be  the  duty  of  the  inspector  and  of  the  contractor 
to  see  that  the  top  surface  of  the  concrete  is  properly  finished, 
so  that  nothing  but  a  horizontal  line  shall  show  on  the  face  of 
the  concrete,  as  the  joint  between  portions  of  the  work  con- 
structed before  and  after  such  period  of  delay.  If  for  any  reason 
it  is  impossible  to  complete  an  entire  layer,  the  end  of  the  layer 
shall  be  made  square  and  true  by  the  use  of  a  temporary  plank 
partition.  No  irregular,  wavy  or  sloping  lines  shall  be  per- 
mitted to  show  on  the  face  of  the  concrete  work  as  the  result 
of  constructing  different  portions  of  the  work  at  different 
periods,  and  none  but  horizontal  or  vertical  lines  shall  be  per- 
mitted in  such  cases." 

ART.   82.     CONCRETE  PILES 

732.  Piles  may  be  made  of  concrete  either  with  or  without 
steel  reinforcement.     In  the  former  case  they  are  built  in  place, 
but  where  steel  is  used  the  piles  are  usually  driven  after  they 


472  CEMENT  AND  CONCRETE 

have  been  prepared  in  suitable  molds.  Concrete  is  also  em- 
ployed to  protect  from  decay,  or  from  the  ravages  of  the  teredo, 
wooden  piles  already  in  service. 

Concrete  piles  are  much  more  durable  than  wooden  piles, 
and  may  be  used  without  reference  to  the  water  line.  A  sav- 
ing may  thus  be  made  under  certain  conditions,  as  the  use  of 
concrete  piles  may  obviate  the  necessity  of  excavating  to  the 
water  line  and  building  up  with  masonry  resting  on  a  wooden 
pile  foundation.  As  the  diameter  of  the  pile  is  not  limited, 
a  much  greater  load  per  pile  may  be  provided  for.  There  are 
of  course  many  places  where  piles  of  concrete  are  not  as  suit- 
able as  wooden  piles;  they  are  not  as  well  adapted  to  with- 
stand certain  kinds  of  hard  usage,  such  as  violent  shocks,  and 
they  are  much  less  flexible. 

733.  Building  in  Place.  —  In  certain  kinds  of  soil,  such  as 
stiff  clay,  a  wooden  pile,  or  dummy,  of  the  proper  length  may 
be  driven  and  withdrawn,  the  hole  left  being  at  once  filled  with 
concrete.     The  application  of  this  crude  method  is  very  lim- 
ited, as  it  is  seldom  that  the  soil  will  stand  until  the  hole  is 
filled  with  concrete. 

For  the  building  of  piles  without  reinforcement,  Mr.  A.  A. 
Raymond  l  has  patented  a  system  by  which  a  thin  steel  shell 
or  casing  is  driven  to  the  desired  depth  and  then  filled  with 
concrete  in  place.  A  shell  is  first  slipped  over  a  steel  pile  core 
made  to  fit  it,  and  the  shell  and  core  are  driven  by  a  pile  driver 
in  the  ordinary  manner.  The  core  is  then  slightly  shrunken 
in  diameter,  by  a  simple  device,  and  withdrawn,  leaving  the 
shell  in  the  ground.  The  core  is  hoisted  in  the  pile  driver 
leaders,  another  shell  is  lowered  into  the  one  just  driven  and 
then  slipped  up  on  the  core,  after  which  the  driver  is  shifted 
to  the  next  location,  and  this  shell  is  driven  in  the  same  manner 
as  the  first.  The  filling  of  the  shells  with  concrete  is  clone  as 
soon  as  convenient.  While  the  shape  of  the  shells  may  be 
varied  to  suit  conditions,  the  ordinary  size  is  about  twenty 
inches  diameter  at  the  top  and  six  inches  at  the  bottom,  and 
such  a  shell  twenty  feet  long  weighs  about  seventy  pounds. 

734.  The    same    company   has   a   system    of    sinking    shells 
in  sand  by  the  water  jet.     For  this  purpose  the  shells  are  in 


Raymond  Concrete  Pile  Co.,  Chicago,  111. 


CONCRETE  PILES  473 

conical  telescopic  sections  about  eight  feet  in  length.  A  two 
and  one-half  inch  pipe  with  three-quarter  inch  nozzle  is  attached 
to  the  center  of  a  cast  iron  point  fixed  to  the  inner  section. 
Water  forced  through  the  pipe  causes  the  shell  to  settle,  and 
as  the  inner  shell  descends,  its  upper  end  engages  with  the  lower 
end  of  the  second  section,  so  that  when  fully  lowered  the  sec- 
tions form  a  continuous  cone.  The  concrete  is  filled  in  simul- 
taneously with  the  sinking,  imbedding  the  two  and  one-half 
inch  pipe  which  remains  permanently  in  the  center  of  the  con- 
crete pile. 

735.  Concrete-Steel  Piles :  Molding.  —  Piles  of  concrete-steel 
usually  have  three  or  more  steel  rods  of  about  one  square  inch 
cross-section  imbedded  longitudinally  in  the  pile,  and  connected 
by   smaller    rods   or   wires    at    intervals   of   six  to  ten  inches. 
Molds  are  so  made  that  they  may  readily  be  detached  and  used 
again.     At  least  one  side  of  the  mold  should  also  be  in  short 
sections  that  may  be  put  in  place  as  needed,  in  order  to  facil- 
itate placing  the  concrete.     The  molds  should  be  set  up  verti- 
cally with  the  longitudinal  steel  rods  in  position.     Enough  con- 
crete is  put  in  the  molds  to  fill  six  to  ten  inches  in  length,  when 
a  set  of  transverse  tie  rods  or  wires  is  placed,  then  another 
layer   of   concrete,   etc.     The   concrete,    which   is   of   Portland 
cement,  should  be  mixed  rather  wet,  as  thorough  tamping  is 
difficult  in  the  confined  space.     The  piles  should  be  provided 
with  a  cast  iron  shoe  at  the  bottom,  or  a  steel  plate  covering 
to  protect  the  point.     At  the  top,  one  of  the  main  rods  is  bent 
over  to  form  a  ring  to  facilitate  handling  the  piles. 

736.  Driving.  —  When    the    concrete    has    hardened    suffi- 
ciently, say-  at  the  end  of  four  to  eight  days,  the  mold  should 
be  removed,  and  the  pile  allowed  to  remain  in  its  original  posi- 
tion twenty  to  twenty-five  days  longer,  sprinkling  it  occasionally. 
When   thoroughly  set,  they  may  be   driven  with  an   ordinary 
pile  driver,  using  a  heavy  hammer  and  short  drop.     A  steam 
hammer  is  preferred,  however,  and  a  special  cap  must  be  used 
to  prevent  injury  to  the  pile  head.     Such  a  special  cap  may 
well    be  made  of  cast  steel,  fitting  over  the    head  of   the  pile 
like  a  helmet.     The  space  between  the  lower  end  of  the  cap 
and  the  side  of  the  pile  is  calked  with  clay  and  rope  yarn  or 
other, suitable  material.     Through  a  hole  provided  in  the  top  of 
the  helmet,  the  space  between  the  pile  and  cap  is  then  com- 


474  CEMENT  AND  CONCRETE 

pletely  filled  with  dry  sand.  Such  a  cushion  cap  effectually 
protects  the  pile  head,  distributing  the  pressure  to  the  entire 
head.  Caps  in  the  form  of  a  steel  ring  filled  with  sawdust  sur- 
mounted by  a  wooden  block,  and  also  caps  made  of  alternate 
layers  of  lead,  wood  and  iron  plates  have  been  successfully 
used. 

ART.  83.    ARCHES 

737.  The  use  of  concrete  in  the  construction  of  arch  bridges 
is  becoming  so  extended  and  diversified  that  it  would  require 
a  volume  by  itself  to  adequately  cover  the  subject,  and  such 
a  treatment  of  it  is  well  merited.     All  that  can  be  attempted 
here  is  to  describe  briefly  one  or  two  examples  of  well  propor- 
tioned arches,  and  to  give  a  few  hints  on  methods  of  design  and 
construction. 

738.  DESIGN.  —  Concrete  arches  may  be  built  with  or  with- 
out steel  reinforcement,   but   for  long   spans    concrete-steel  is 
usually  employed.     The  design  of  a  concrete  arch  without  steel 
is  entirely  similar  to  that  of  a  stone  masonry  arch,  except  that 
planes  of  weakness  corresponding  to  joints  between  voussoirs 
in  a  masonry  arch,  may  be  somewhat  more  arbitrarily  arranged 
in  the  former. 

In  fixed  concrete-steel  arches,  the  arch  ring  is  continuous, 
and  is  capable  of  resisting  a  bending  moment.  The  compu- 
tations are  therefore  somewhat  more  complicated,  and  until  the 
action  of  concrete  and  steel  in  combination  has  been  more 
carefully  determined,  it  may  be  said,  in  the  words  of  a  promi- 
nent engineer,  that  "the  development  of  the  system  of  arches 
of  concrete  must  necessarily  be  largely  based  upon  empirical 
information  coupled  with  sound  judgment  and  wo'rk  executed 
with  great  care."  '  Fortunately,  the  saving  effected  by  this  con- 
struction over  a  masonry  arch  is  usually  so  great  that  it  is 
possible  to  use  a  large  factor  of  ignorance,  and  it  is  to  be  hoped 
that  the  use  of  concrete-steel  for  arches  of  long  span  will  not  be 
given  a  serious  check  by  the  failure,  perhaps  under  unforeseen 
conditions,  of  some  of  the  web-like  structures  that  have  been 
built  of  it. 

739.  Where  the  span  and  rise  of  the  arch  are  not  fixed  by 
the    local    conditions,    the    comparative    economy    of   different 


1  L.  L.  Buck,  Trans.  A.  S.  C.  E.;  April,  1894. 


ARCHES  475 

arrangements  and  the  appearance  of  the  completed  structure 
must  govern.  Shortening  the  spans  decreases  the  amount  of 
concrete  required  in  the  arches,  but  increases  the  pier  work, 
which  is  usually  the  most  expensive  part  of  the  structure. 

These  points  having  been  decided,  the  form  to  be  given  the 
arch  ring  is  next  to  be  considered.  While  it  is  desirable  that 
the  neutral  axis  of  the  arch  ring  should  nearly  correspond  with 
the  line  of  pressures  for  a  full  load,  there  is  still  considerable 
choice  allowed  the  designer  as  to  the  actual  form  to  be  given 
the  intrados  without  serious  changes  in  the  amount  of  material 
required.  As  the  semicircular  arch  can  usually  be  adopted 
for  very  short  spans  only,  the  choice  must  lie  between  the  seg- 
mental,  the  elliptical,  and  the  polycentered  arch  approaching 
more  or  less  closely  the  ellipse,  the  parabola,  or  the  transformed 
catenary. 

The  segmental  arch,  the  parabola  and  the  catenary  do  not 
give  a  pleasing  effect  at  the  junction  of  the  arch  ring  and  the 
abutment,  and  the  curve  is  sometimes  departed  from  near  the 
springing  to  make  the  intrados  tangent  to  the  face  of  the  abut- 
ment. The  final  choice  will  thus  usually  lie  between  a  true 
ellipse  and  the  basket-handled  arch. 

Mr.  Edwin  A.  Thacher,  M.  Am.  Soc.  C.  E.,  designer  of  the 
Topeka  bridge,  considers  that  "arches  with  solid  spandrel  fill- 
ing should  be  flat  at  the  center  and  sharper  at  the  ends,  ap- 
proaching an  ellipse;  while  arches  with  open  spandrel  spaces 
should  be  sharp  at  the  center  and  flatter  at  the  ends  approach- 
ing a  parabola,  or,  which  is  better,  sharp  at  the  ends  and  center 
and  flat  at  the  haunches."  1 

The  form  of  the  intrados  having  been  fixed,  the  depth  of  key- 
stone for  an  arch  without  reinforcement  is  derived,  tentatively, 
from  the  rules  of  either  Rankin  or  Trautwine,  to  be  corrected 
later  if  necessary.  The  form  of  the  extrados  is  then  so  chosen 
as  to  give  the  required  depth  of  arch  ring  to  confine  the  line  of 
pressure  within  the  middle  third. 

740.  Concrete-steel  Arch.  —  The  computation  of  a  concrete- 
steel  arch  is,  as  already  stated,  more  involved.  The  graphical 
analysis  is  much  the  simplest  method  of  deriving  the  bending 
moment,  direct  thrust  and  shear.  The  experience  of  Mr. 


Engineering  News,  Sept.  21,  1899. 


476  CEMENT  AND  CONCRETE 

Thacher  has  led  him  to  endeavor  to  have  the  line  of  pressure  lie 
within  the  middle  third  of  the  arch  ring,  although  this  is  not 
absolutely  necessary  in  reinforced  concrete.  The  same  author- 
ity considers  it  good  practice  to  design  the  steel  work  to  be 
capable  of  taking  the  entire  bending  moment  with  a  unit  stress 
of  about  one-half  the  elastic  limit  of  the  steel. 

The  thrusts,  bending  moments  and  shears  at  successive  sec- 
tions of  the  arch  ring  having  been  determined,  both  for  full 
and  half  span  loads,  by  the  graphical  methods  explained  in 
Greene's  "  Arches"  or  Cain's  " Elastic  Arches,"  or  by  the  analy- 
sis given  in  Howe's  " Treatise  on  Arches,"  the  dimensions  of  the 
arch  ring  and  the  steel  reinforcement  are  to  be  derived  by 
the  aid  of  such  formulas  as  are  given  by  Mr.  Thacher1  involving 
the  allowable  unit  stresses  in  steel  and  concrete,  and  their 
respective  moduli,  of  elasticity. 

741.  General  Considerations.  —  In  short  spans,  parallel 
spandrel  walls  with  earth  filling  between,  may  be  used,  but 
for  long  spans  the  spandrels  are  usually  open,  that  is,  built 
of  vertical  piers  or  walls  running  parallel  to  the  axis  of  the 
soffit,  and  arched  over  at  the  top  to  support  the  pavement  or 
ballast.  This  treatment  has  the  following  advantages:  only 
vertical  forces  are  transmitted  to  the  arch  ring;  decreased 
loads  on  arch  and  abutments;  increased  waterway  in  case  of 
unusual  floods;  and  better  architectural  effects. 

The  beauty  of  the  structure  is  an  important  consideration, 
inasmuch  as  the  decision  in  favor  of  a  concrete  arch  as  against 
a  steel  bridge  is  usually  affected  quite  as  much  by  considera- 
tions of  aesthetic  effect  as  of  cheapness  and  durability.  In 
this  connection  it  may  be  said  that  in  concrete-steel  construc- 
tion there  may  be  little  difference  in  the  thickness  of  arch  ring 
required  at  the  crown  and  near  the  springing,  but  the  appear- 
ance of  the  structure  will  usually  be  improved  by  accentuating 
a  little,  if  necessary,  the  increased  thickness  at  the  springing, 
except  in  the  case  of  the  semicircular  arch  in  which  the  eye  is 
accustomed  to  a  nearly  uniform  thickness  of  the  voussoirs. 
The  appearance  is  also  frequently  improved  by  molding  the 
concrete  at  the  crown  to  represent  a  keystone,  projecting  a 
little  beyond  the  face  of  the  rest  of  the  arch  ring. 


1  Engineering  News,  Sept.  21,  1899. 


ARCHES  477 

The  beauty  of  a  concrete  arch  may  easily  be  marred  by 
faulty  design,  and  some  very  ugly,  as  well  as  some  very  beau- 
tiful, arches  have  been  erected. 

742.  Stone  Facing.  —  The  practice  which  has  been  followed 
to  some  extent  of    facing  the  spandrel   walls  with  cut  stone 
masonry,  is  considered  questionable.     The  cost  of  ashlar  facing 
is  likely  to  be  so  great  as  to  discourage  the  use  of  headers  of 
sufficient  length  to  give  a  good  bond  with  the  concrete,  and  it 
is  next  to  impossible  to  make  this  equal  to  monolithic  concrete 
construction.     Again,  since  concrete  is  frequently  used  to  pro- 
tect ashlar  masonry  that  has  started  to  disintegrate,  it  is  rather 
a  reversal  of  what  has  been  found  good  practice  to  face  con- 
crete with  a  thin  layer  of  cut  stone.     No  criticism  is  intended 
of  the  method  of  building  a  pier  of  large  dimension  stone  with 
concrete  hearting,   as  this  is  a  different  matter.     But  a  thin 
parapet  or  spandrel  wall  faced  with  a  mere  shell  of  cut  stone, 
however  beautiful  it  may  be  when  built,  is  likely  to   take  on  a 
somewhat  dilapidated  appearance  after  ten  years'  service,  espe- 
cially if  it  is  called  upon  to  pass  through  one  or  two  floods  of 
unusual  violence. 

743.  Quality  of  Concrete.  —  As  already  intimated,  the  cost 
of  a  concrete  arch,  especially  where  reinforcement  is  used,  is, 
under  ordinary  circumstances,  considerably  less  than  a  masonry 
arch  of  equal  appearance  and  strength.     The  only  exceptions 
to  this  rule  are  where  the  facilities  for  obtaining  stone  suitable 
for  masonry  are    exceptional,  and  where    the  work    is   far  re- 
moved  from   cement-producing   regions   and   from    the    coast. 
The  ability  to  employ  common  labor  for  much  of  the  construc- 
tion work  in  a  concrete  arch  is  an  advantage  only  partially 
offset  by  the  necessity  of  having  somewhat  more  careful  work 
done  upon  the  arch  centers  and  more  careful  supervision  of 
construction. 

The  concrete  of  the  arch  ring  should  be  of  the  best  quality, 
especially  if  steel  reinforcement  is  not  used.  For  this  purpose, 
the  stone,  broken  to  a  size  not  exceeding  two  inches  in  any 
dimension,  should  be  mixed  with  a  quantity  of  mortar  a  little 
more  than  sufficient  to  fill  the  voids,  and  composed  of  one  part 
Portland  cement  to  two  parts  sand.  Interiors  of  piers  and 
abutments  may  be  made  of  a  poorer  mixture,  such  as  one 
Portland  cement  to  three  of  sand  and  six  of  broken  stone,  or 


478  CEMENT  AND  CONCRETE 

even  in  some  cases  where  abutments  are  massive,  one  to  four 
to  eight  concrete  may  be  employed. 

744.  Centers.  —  Substantial    centers   must   be   provided   for 
concrete  arches,  and  the  lagging  should  be  sized,  dressed  on  the 
upper  side,  and  laid  with  radial  joints  parallel  to  the  arch  axis. 
Two  inch  plank  sized  to  one  and  three-quarters  inches  is  usually 
employed  for  lagging,  and  the  supporting  ribs  should  be  from 
three  to  four  feet  centers.     For  spans  up  to  forty  feet  a  braced 
wooden  rib  with  one  center  support  and  two  end  supports  is 
used,  but  for  longer  spans  a  trussed  center  with  supports  ten  to 
eighteen  feet  apart  is  employed.     The  centers  should  be  made 
rigid  and  the  camber  need  be  very  slight,  say  from  T^TT   to 
^^   of  the  radius  at  the  crown.     Not  less  than  twenty-eight 
days  should  be  allowed  to  elapse  after  building  the  arch  before 
striking  the  centers. 

745.  Construction.  —  A  method  that   has  been  largely  em- 
ployed in  building  the  arch  ring  is  to  divide  the  arch  into  lon- 
gitudinal rings  by  planes  at  right  angles  to  the  arch  axis.     It 
is  believed  to  be  better  practice,  however,  to  build  the  arch  as 
a  series  of  voussoir  courses  beginning  with  the  spring  course, 
but  not  necessarily  proceeding  in  order  from  the  springing  to 
the   crown.     The   advantages   of  this   method   of  building  the 
arch,  in  transverse  courses  parallel  to  the  axis  of  the  intrados, 
are  that  the  planes  of  weakness  may  be  made  at  right  angles 
to  the  line  of  pressure;  the  unequal  loading,   and  consequent 
settlement  of  the  centers,  has  less  tendency  to  crack  the  sec- 
tions  or  to   separate   one   section  from   another.     In   cases   of 
failure  of  concrete  arches  under  excessive  floods,  the  tendency 
of  the  arch  to  separate  along  a  longitudinal  joint  forming  a 
plane  of  weakness  has  been  clearly  shown. 

746.  The  tendency  of  the  center  to  rise  at  the  crown  as  the 
arch  ring  is  built  up  on  the  haunches  is  sometimes  overcome  by 
temporarily  loading  the   crown.     In   constructing   the   ring   in 
voussoir  courses,  the  order  of  the  work  may  be  so  arranged  as 
to  distribute  the  loading  on  the  centers  in  any  manner  desired. 
Such   an   expedient   was   adopted   in   the   construction   of   the 
Illinois  Central  R.  R.  arch  across  Big  Muddy  River,  where  the 
arch  ring  was  divided  into  nineteen  voussoirs.     The  two  spring- 
ers were  built  first,  then  the  fifth  row  of  voussoirs  towards  the 
crown  on  each  side,  followed  by  the  ninth  row,  the  third  and 


ARCHES  479 

seventh.  The  intermediate  blocks  were  then  built  in  order 
toward  the  crown,  the  second,  fourth,  sixth  and  eighth,  and 
finally  the  keystone.  In  this  way  the  weight  was  well  dis- 
tributed on  the  centers,  and  the  load  on  the  two  sides  of  the 
crown  was  kept  symmetrical.  The  monolithic  blocks  forming 
the  voussoirs  that  were  built  in  molds  had  recesses  on  either 
side,  which  were  made  by  securing  planks  to  the  interior  of 
the  mold.  When  the  intermediate  blocks  were  built,  the  con- 
crete thus  keyed  into  the  blocks  first  made. 

The  division  of  the  work  into  voussoir  courses  will  usually 
admit  of  such  size  molds  or  blocks  that  two,  one  on  either  side 
of  the  center,  may  be  completed  in  a  day.  If  it  becomes  ne- 
cessary to  interrupt  the  laying  of  a  block,  however,  a  vertical 
bulkhead  should  be  constructed  in  the  mold,  with  key  or  dowel 
pins  if  desired,  to  assist  in  making  a  bond  when  the  block  is 
completed. 

747.  Finish  and  Drainage.  —  To  provide  a  smooth  face,  a 
thin  facing  mortar  of  one  part  Portland  to  two  parts  sand  is 
desirable,  laid  at  the  time  of  building  the  concrete  in  accord- 
ance with  methods  already  described.  A  thicker  layer  of 
granolithic  may  be  used  on  the  soffit  and  will  somewhat  more 
effectually  prevent  the  broken  stone  of  the  concrete  settling  on 
the  lagging,  which  is  always  likely  to  occur  to  the  detriment 
of  the  appearance  of  the  finished  work. 

The  division  between  adjacent  voussoirs  should  be  clearly 
marked  on  the  face,  and  additional  joints  may  be  indicated  if 
desired,  by  lines  in  a  plane  approximately  perpendicular  to  the 
line  of  pressure.  Such  lines  are  obtained  by  securing  triangular 
strips  on  the  inner  face  of  the  molds.  When  spandrel  walls  are 
used,  these  may  be  similarly  marked  on  the  face  by  horizontal 
and  vertical  joints.  On  long  spans  the  spandrels  should  have 
expansion  joints,  and  the  coping  and  parapet,  when  of  concrete, 
should  also  have  vertical  joints  to  provide  for  changes  in  length 
due  to  loading  or  thermal  variations. 

The  arches  over  the  spandrels  should  be  provided  with  a 
waterproof  covering,  either  of  Portland  cement  grout  or  an 
asphalt  mixture  to  prevent  the  percolation  of  water  to  the  arch 
ring.  Pipe  drains  should  be  provided  to  carry  the  water  to  a 
point  over  the  piers  where  it  may  be  discharged.  Care  should 
be  taken  that  such  pipes  have  their  outlets  so  located  that  the 


480  CEMENT  AND  CONCRETE 

drip  shall  not  disfigure  the  wall.     Open  spandrels  may  be  drained 
by  pipes  built  into  the  arch  ring  at  suitable  places. 

748.  Highway  Arch  without  Reinforcement.  —  A  good   ex- 
ample of  a  highway  bridge  built  of  concrete  without  reinforce- 
ment is  the  monolithic  arch  spanning  San  Lea'idro  creek,  be- 
tween Oakland  and  San  Leandro,  Cal.1     This  arch  has  a  five 
centered,  elliptical  intrados,  with  span  of  81|  feet,  rise  of  26 
feet  and  width  of  about  60  feet.     At  the  crown  the  thickness 
of  the  arch  ring  is  3  feet,  the  radius  of  the  intrados  61  i  feet  and 
of  the  extrados  88  feet. 

As  the  arch  rests  directly  on  a  bed  of  clay  containing  some 
gravel,  the  footings  are  made  30  feet  wide,  and  they  extend 
5  feet  below  the  creek  bed.  The  lagging  for  the  forms  was 
of  2  by  6  inch  scantling  laid  transverse  to  the  axis  of  the 
structure  or  parallel  to  the  axis  of  the  intrados.  The  ribs  of 
the  centering  were  built  of  two  1  by  12  inch  boards  and  the 
braces  of  4  by  6  inch  timbers,  converged  to  three  short  12  by 
12  inch  timbers  supported  by  wedges  bearing  on  12  by  12 
inch  longitudinals. 

749.  The   concrete   was    composed   of   one   barrel    Portland 
cement,  two  barrels  sand  to  seven  barrels  of  broken  stone  of 
varying  sizes. 

When  the  haunches  had  been  built  up  about  one-third  the 
way,  as  flooding  of  the  work  was  anticipated,  an  arch  ring  one 
foot  thick  was  first  completed,  the  remainder  being  placed  as 
a  second  layer.  There  is  a  parapet  wall  three  feet  six  inches 
high  on  either  side  of  the  bridge.  The  spandrel  walls  show  a 
solid  face,  and  are  paneled  to  bring  out  the  outlines  of  the 
extrados  and  parapet.  The  centers  were  struck  ten  days  after 
the  completion  of  the  second  arch  ring,  and  the  settlement  at 
the  crown  was  about  one  and  one-half  inches.  The  forms  con- 
tained 90,000  feet,  B.  M.,  of  lumber,  and  3,384  cubic  yards  of 
concrete  were  used.  The  cost  of  the  bridge  was  $25,840.00, 
or  less  than  $8.00  per  cubic  yard  of  concrete.  The  contractors 
were  the  E.  B.  and  A.  L.  Stone  Co.  of  Oakland,  Cal.,  and  the 
plans  were  prepared  by  the  County  Surveyor's  office  of  Alameda 
County,  Cal. 

750.  A  Three  Span  Arch.  —  The  three  span  arch  spanning  a 


1  Described  by  Mr.  William  B.  Barber,  Engineering  News,  Aug.  27,  1903. 


ARCHES  481 

mill  pond  on  Anthony  Kill,  near  Mechanicsville,^  N.  Y.,1  is 
worthy  of  notice  on  account  of  some  peculiarities  in  the  center- 
ing and  because  of  the  location  of  the  plant  on  a  side  hill,  so 
that  the  concrete  was  delivered  on  the  work  with  very  little 
labor.  Two  of  the  arches  were  of  100  ft.  span,  with  rise  of 
20  feet,  and  the  remaining  arch  was  of  50  ft.  span.  The  width 
is  but  17  feet,  and  the  piers  are  founded  on  rock  at  a  depth  not 
exceeding  12  feet. 

For  the  centering,  piles  were  first  driven,  six  feet  centers, 
in  bents  ten  feet  apart,  and  the  bents  capped  with  ten  by  twelve 
inch  timbers.  Stringers  of  the  same  dimensions  were  then  laid 
longitudinally,  and  eight  by  ten  inch  posts  were  erected  on  the 
longitudinals  and  spaced  three  feet  center*.  These  posts, 
which  were  cut  to  proper  length,  so  that  their  tops  conformed  to 
the  curve  of  the  intrados,  were  then  capped  with  eight  by  ten 
inch  timbers  parallel  to  the  axis  of  the  intrados,  and  the  lagging 
laid  upon  them  transverse  to  this  axis  or  parallel  to  the  center 
line  of  the  bridge.  This  lagging  was  of  two  thicknesses  of  one 
inch  boards  sprung  into  place  and  nailed,  the  upper  layer  being 
of  dressed  lumber  to  give  a  smooth  surface  to  receive  the  con- 
crete. 

The  concrete  was  of  one  part  Portland  cement,  three  parts 
sand,  three  parts  gravel  and  three  parts  broken  stone,  except 
for  the  arch  ring,  in  which  but  two  and  one-half  parts  each  of 
gravel  and  stone  were  used.  The  concrete  plant  was  so  ar- 
ranged that  the  stone  could  be  passed  from  the  crusher  to  the 
mixer  by  gravity.  The  concrete  was  delivered  on  the  arch  in 
cars  of  three  feet  gage  drawn  by  cable.  From  fifty  to  sixty 
cubic  yards  of  concrete  were  placed  in  ten  hours  with  but  nine 
laborers.  140,000  feet  B.  M.  lumber  was  used  in  centers. 
The  entire  work  consumed  about  2,500  cubic  yards  of  concrete. 

751.  Railroad  Arch  without  Reinforcement.  —  The  concrete 
bridge  carrying  the  Illinois  Central  R.  R.  over  the  Big  Muddy 
River  furnishes  an  excellent  example  of  a  long  span  arch,  built 
without  reinforcement  so  far  as  the  arch  ring  is  concerned. 
The  bridge  is  very  fully  described  by  Mr.  H.  W.  Parkhurst, 
Engineer  of  Bridges  and  Buildings  I.  C.  R.  R.,  in  Engineering 
News  of  Nov.  12,  1903.  There  are  three  spans,  each  140  feet 

1  Described  in  Engineering  News,  Nov.  5,  1903. 


482  CEMENT  AND  CONCRETE 

in  the  clear,  with  30  feet  rise  above  springing  lines.  The  arch 
ring  proper  is  five  feet  thick  at  the  crown,  but  as  the  spandrels, 
which  are  built  open  over  the  haunches,  have  near  the  crown 
only  a  false  opening  on  the  face,  the  actual  thickness  of  concrete 
at  the  crown  is  seven  feet. 

The  piers  and  abutments  already  in  place  for  the  three 
Pratt  trusses  formerly  in  use,  were  surrounded  with  new  con- 
crete masonry,  making  the  piers  21  ft.  6  in.  wide  at  the  top. 
As  rock  was  found  only  at  considerable  depth,  the  piers  rested 
on  piles.  To  relieve  the  load  on  foundations  as  much  as  possible, 
as  well  as  to  avoid  cracking,  which  would  be  likely  to  occur  in 
heavy  longitudinal  spandrel  walls  from  temperature  strains, 
transverse  spandrel  arches  were  adopted.  Since  in  case  of  de- 
railment of  trains  these  spandrel  arches  would  be  subjected  to 
shock,  the  concrete  in  this  portion  of  the  structure  was  rein- 
forced by  a  self-supporting  skeleton  structure  built  of  steel 
rails.  Longitudinal  rails  were  laid  horizontally,  three  feet 
center  to  center,  connected  at  frequent  intervals  by  one  inch 
rods  and  held  in  place  by  vertical  posts,  which  in  turn  rested 
upon  transverse  horizontal  rails  laid  in  recesses  left  in  the  arch 
rib. 

752.  Expansion  joints  were  provided  in  the  spandrel  arches 
at  the  ends,  two  at  each  pier  and  one  at  each  abutment,  to  al- 
low some  movement  due  to  changes  in  temperature.     The  ex- 
pansion joints  were  made  by  placing  in  the  joint  several  thick- 
nesses of  corrugated  asbestos  board  protected  by  a  J-inch  lead 
plate  folded  into  the  joint,  forming  a  trough  at  the  top.     The 
lead  plate  lies  flat  on  top  of  the  concrete  for  five  inches  from 
the  joint,  and  about  two  inches  at  each  end  of  the  plate  is  bent 
down  at  right  angles  and  set  into  the  concrete.     An  asphaltic 
composition  is  then  laid  over  the  lead  plate,  entirely  covering 
it  and  filling  the  trough. 

The  centering  was  erected  on  pile  bents  spaced  about  14 
feet  centers,  the  calculated  pressure  on  each  pile  being  about 
eighteen  to  twenty  tons.  For  the  center  span,  five  60  foot 
deck  plate  girders  resting  on  pile  piers  were  used  over  the  deep- 
est portion  of  the  channel  to  provide  for  possible  floods  bring- 
ing large  amounts  of  drift. 

753.  The  arch  ring  was  laid  in  voussoir  courses  as  described 
in  §  746.     Face  joints  were  made  by  securing  triangular  shaped 


ARCHES  483 

pieces  to  inner  face  of  the  molds  in  lines  approximately  at 
right  angles  to  the  line  of  pressure.  All  exposed  work  was 
faced  with  a  layer  of  about  1^  inches  of  Portland  cement  mortar 
placed  and  rammed  with  the  concrete.  The  surfaces  were  not 
given,  in  general,  any  further  finish,  no  attempt  being  made  to 
remove  or  conceal  the  usual  marks  left  by  the  mold  boards. 

Portland  cement  was  used  throughout,  the  quality  of  the 
concrete  being  varied  by  the  amount  of  cement  used  to  given 
quantities  of  the  aggregates.  In  the  centers  of  large  masses 
the  poorer  mixtures  were  employed,  while  the  richer  concretes 
were  used  in  those  places  subjected  to  the  most  trying  conditions. 

In  making  the  concrete  the  principle  followed  seems  to  have 
been  to  keep  the  mixer  as  near  the  work  as  practicable,  moving 
the  mixer  and  carrying  materials  to  it,  rather  than  to  transport 
the  mixed  concrete  from  a  certain  fixed  location  of  the  mixing 
plant.  Much  of  the  concrete  was  handled  in  barrows,  but 
derricks  were  also  used  in  portions  of  the  work.  As  traffic  on 
the  old  bridge  had  to  be  maintained  during  the  erection  of  the 
new  structure,  considerable  extra  handling  of  concrete  was 
necessary  and  additional  work  was  involved  in  ramming  the  con- 
crete in  places  difficult  of  access.  The  concrete  was  mixed  rather 
wet,  so  that  but  little  tamping  was  required  to  make  it  quake. 

754.  Cost.  —  The  total  amount  of  concrete  was  over  12,000 
cubic  yards,  which  was  placed  at  an  average  cost  of  $5.43  per 
cubic  yard.     In  cofferdams  and   centers  400,000  feet  B.  M.  of 
timber  was  used,  and  about  300,000  pounds  of  steel  was  em- 
ployed in  the  skeleton  structure  of  the  spandrels.     This  steel 
cost   1.2  cents  per  pound,  the  punching,  fitting  and  erecting 
costing  but  about  0.61  cent  per  pound.     The  total  cost  of  the 
bridge   is  estimated   to    have   been  $125,000.00,  or   about   the 
same  as  the   estimated  cost  of    a  steel   structure  designed  for 
the  same  duty. 

755.  The  Melan  Arch  Bridge  at  Topeka,  Kan.,  is  one  of  the 
most   important    concrete-steel    structures   yet   erected   in   the 
United   States.     It   consists  of  one  span  of   125  feet,   two  of 
110  feet  each,  and  two  of  97.5  feet  each.     The  foundations  for 
piers   and   abutments   are   piles  in  soft  sand.     The  steel  rein- 
forcement is  in  the  form  of  a  latticed  member.     The  bridge  is 
fully  described  in  Engineering  News  of  April  2,  1896,  and  En- 
gineering Record,  April  16,  1898, 


484  CEMENT  AND  CONCRETE 

756.  Concrete-Steel  Viaduct.  —  A  viaduct  of    ten  concrete- 
steel  arches,  of  about  65  foot  span,  carries  a  double  track  elec- 
tric line  across  West  Canada  Creek  near  Herkimer,  N.  Y.1     The 
piers  rest  on  piles  driven  into  hard  blue  clay,  the  surface  of 
which  is  6  to   12  feet  below  the   creek   bed.     The   segmental 
arches  have  a  rise  of  12  to  14  feet,  with  thickness  of  21  inches 
at  the  crown  and  4^  feet  at  the  springing;  the  radius  of  intrados 
is  about  46  feet,  and  of  extrados  about  57  feet.     The  stresses 
were  computed  for  full  load  and  for  live  load  on  half  span, 
Prof.  Cain's  graphical  method  being  employed.     The  maximum 
stresses  allowed  were  six  hundred  pounds  per  square  inch  com- 
pression in  concrete  and  ten  thousand  pounds  per  square  inch 
tension  in  steel.     The  stresses  caused  by  a  variation  of  fifty 
degrees  in  temperature  were  allowed  for.     The  tensile  strength 
of  the  concrete  was  disregarded.     Thacher  bars,  1J  inches  dia- 
meter,  were   used   for   the   reinforcement,  being   placed   eleven 
inch  centers  near  both  intrados  and  extrados. 

757.  Expansion    joints   were  provided  in  spandrel  walls  by 
nailing  to  the  sides  of  the  forms  for  arch  pilasters  a  narrow 
strip  of  timber,  thus  forming  a  groove  into  which  the  spandrel 
wall  is  tongued.     These  joints  show  some   motion   and   allow 
some  water  to  leak  through. 

The  concrete  was  mixed  three  parts  sand  and  seven  parts 
gravel  to  one  volume  packed  cement  for  foundations  and  piers, 
and  two  and  one-half  parts  sand  and  five  of  gravel  to  one  ce- 
ment for  the  arch  rings  and  spandrel  walls.  All  concrete  was 
mixed  wet  and  by  hand.  The  work  was  faced  with  mortar 
composed  of  one  part  cement  to  two  and  one-half  parts  sand, 
and  after  the  removal  of  forms  the  face  was  brushed  with  thin 
mortar  wash  and  rubbed  with  sandstone  blocks,  giving  a  uni- 
form color  to  the  surface. 

ART.  84.     DAMS 

758.  Concrete  vs.  Rubble.  —  Concrete  has  been  employed  to 
some  extent  in  most  of  the  important  masonry  dams  of  recent 
construction,  and  has  formed  the  main  portion  of  some  of  the 
largest  dams  yet  built. 

The  relative  value  of  concrete  and  uncoursed  rubble  masonry 


Engineering  News,  Feb.  27,  1904. 


DAMS  485 

laid  in  Portland  cement  mortar  is  perhaps  still  an  open  ques- 
tion, though  it  is  believed  that  the  former  will  eventually  be 
preferred  by  engineers  who  are  familiar  with  both.  Concrete 
will  require  in  general  a  larger  proportion  of  cement  than  does 
the  masonry,  so  that  in  localities  difficult  of  access,  the  ma- 
sonry may  for  this  reason  be  cheaper.  Usually,  however,  con- 
crete will  be  the  cheaper,  and  less  skilled  labor  will  be  required 
in  the  building.  With  the  same  amount  of  inspection,  concrete 
of  good  materials  properly  proportioned  will  form  at  least  as 
impervious  a  wall  as  will  rubble. 

759.  Quality  of  Concrete.  —  The  up-stream  face  of  the  dam 
should  be  made  as  nearly  water-tight  as  possible,  and  therefore 
a  rich  concrete  employed  in  which  the  mortar  is  in  excess  of 
the  voids  in  the  stone,   and  the  mortar  itself  contains  about 
two  parts  sand  to  one  cement.     The  body  of  the  wall,  however, 
may  be  made  of  a  poorer  mixture,  one  to  three  to  six  usually 
being  sufficient.     Bowlders  may  also  be   imbedded  in  the  mass 
to  cheapen  the  concrete  without  any  serious  detriment.     Such 
bowlders  should,  of  course,  be  sound  and  clean,  and  well  wet 
before  being  placed.     They  should  be  kept  well  back  from  the 
face  of  the  wall  and  should  be  separated  one  from  another  by 
at  least  six  inches,  to  allow  of  thoroughly  tamping  the  concrete 
between  them. 

760.  Building  in  Sections.  —  In  a  wall  of   rubble  the  con- 
traction and  expansion  are  taken   care  of  by   minute   cracks 
between  the  stone  and  mortar  which  frequently  are  not  notice- 
able.    In  a  concrete   wall,   unless  provision  is   made  for  this, 
these  signs  of  movement  may  be  concentrated  in  cracks  at  in- 
tervals of  thirty  to  sixty  feet;  these  are   always  unsightly,  and 
may   in   exceptional   cases   be   a   serious   defect.     The   remedy 
evidently  lies  in  so  building  the  dam  that  if  these  cracks  appear, 
they  shall  be  confined  to  predetermined  planes  where  they  will 
not   do   any   serious   harm.     Such    contraction    cracks   will   be 
very  much  less  likely  to  occur  in  a  dam  arched  in   plan  than 
in  a  straight  dam,  since  in  the  former  a  slight  movement  of  the 
masonry  up  or  down  stream  changes  the  length  of  the  wall 
and  relieves  the  tension  strains. 

761.  Joints.  —  The   joints  in  a  concrete  dam  should  not  be 
unbroken  planes  for  any  great  distance.     That  is,  the  concrete 
should  be  so  placed  that  the  joints  between  work  of  different 


48G  CEMENT  AND  CONCRETE 

days  are  not  planes  extending  through  the  wall.  The  wall 
may  well  be  kept  higher  on  the  down-stream  side  and  step  down 
toward  the  up-stream  side.  The  vertical  joints  should  also  be 
broken  by  right-angled  off-sets,  but  the  wisdom  of  using  a  dove- 
tail joint  in  such  work  is  very  questionable.  The  joining  of 
one  day's  work  to  another  necessarily  forms  a  plane  of  weak- 
ness, and  therefore  the  work  should  be  carefully  planned  to 
the  end  that  these  planes  shall  be,  in  direction  and  location, 
where  they  will  not  unnecessarily  weaken  the  structure  or  render 
it  pervious  to  water. 

762.  Examples:  St.  Croix  Dam.  —A  dam  at  St.  Croix,  Wis.,1 
was  built  of  sandstone  masonry  of  uncoursed  rubble  in  one-to- 
three  mortar,  and  faced  with  concrete  of  one  Portland  cement 
to  three  parts  sand  to  four  parts  broken  stone  of  1  to  3^  inch 
size.     The  concrete  was  rammed  in  place  between  the  stone- 
work and  the  concrete  forms.     The  selection  of  the  uncoursed 
rubble  was  probably  made  on  account  of  the  site  being  five 
miles  from  the  railway  and  the  consequent  difficulty  of  getting 
cement.     The  dam  was  arched  in  plan,  and  in  preparing  the 
foundation,  several  grooves  or  trenches  were  cut  in  the  rock  in 
a  longitudinal  direction,  to  avoid,  as  usual,  a  through  course  at 
the  bottom,  and  these  trenches  were  also  filled  with  concrete. 
Had  the  concrete  for  the  facing-  contained  five  parts  of  broken 
stone  having  maximum  size  of  2  or  2J  inches,  it  would  have 
been  more  nearly  in  conformity  with  the  best  practice. 

763.  Massena  Dam.  —  In  the  construction  of  the  dam  at  the 
forebay  of  the  Massena  Water  Power  Company,  Massena,  N.Y.,2 
it  was  sought  to  take  up  the  tension  stresses  due  to  contrac- 
tion by  imbedding  in  a  longitudinal  direction  in  the  concrete, 
T-rails   two  feet  apart  horizontally  and  four  feet  apart  ver- 
tically. 

764.  Butte   Dam.  —  The  dam  built  in   connection  with  the 
Butte,  Montana,  water  system  is  120  feet  high,  350  feet  long, 
10  feet  wide  at  the  top  and  83  feet  wide  at  the  120  foot  point. 
The  bed  rock  was  granite,  which  was  first  covered  with  four 
inches  of  concrete  made  with  small  sized  stone.     In  the  body 
of  the   dam,  granite  bowlders   were  thickly  imbedded  in  the 


1  Engineering  News,  June  13,  1901. 

2  Engineering  News,  Feb.  21,  19.01. 


DAMS  487 

concrete,  care  being  taken  that  each  bowlder  was  entirely  en- 
veloped in  concrete  and  that  there  were  no  horizontal  or  nearly 
horizontal  courses  either  of  concrete  or  bowlders. 

765.  San  Mateo  Dam.  —  The  San  Mateo  Dam  of  California, 
one  of  the  highest  dams  in  existence,  is  built  entirely  of  concrete, 
170  feet  high.     It  is  126  feet  thick  at  the  base  and  is  arched  up- 
stream with  a  radius  of  637  feet.     The  dam  was  constructed  in 
blocks  of  200  to  300  cubic  yards  each,  of  irregular  heights,  so  as 
to  bond  the  courses  together  and  have  no  through  joints.     Con- 
crete, one,  two  to  six,  was  delivered  in  small  push  cars  on  a 
high  trestle  over  the  dam,  and  was  dropped  through  iron  pipes 
16   inches   in   diameter   to   the   place   of   deposition.     In   some 
cases  this  drop  was  120  feet,  and  it  is  stated  that  the  concrete 
appeared  not  to  be  injured  by  this  method  of  handling. 

766.  Barossa    Dam.  —  The    Barossa    Dam    in    South    Aus- 
tralia 1  is  of  a  bold  arch  design.     The  arch  has  a  radius  of  200 
feet,  and  the  chord  is  370  feet  subtending  an  angle  of  135  degrees, 
20  minutes,  and  the  length  of  the  arc  472  feet.     The  height  of 
the  dam  is  94  feet  above  the  ground  line,  yet  the  greatest  thick- 
ness above  the  foundation  is  only  34  feet,  with  a  top  width  of 
only  4£  feet. 

Special  care  was  taken  in  selecting  the  materials  and  fixing 
the  proportions.  The  cement  was  aerated  fourteen  days  before 
use.  Test  cubes  of  concrete  two  feet  on  a  side  were  prepared 
with  different  proportions  of  materials  and  subjected  to  a 
hydrostatic  pressure  of  two  hundred  feet  before  deciding  upon 
the  proportions  to  use  in  the  concrete.  As  a  result  of  these 
tests,  the  aggregate  was  made  up  of  one  part  screenings  J  to 
J  inch,  two  parts  "nuts"  J  to  1J  inch,  and  four  and  one-half 
parts  "metal"  1J  to  2  inch.  This  mixture  contained  about  35 
per  cent,  voids.  The  mortar  was  made  of  one  part  Portland 
cement  to  one  and  one-half  parts  sand,  and  was  from  seven  and 
one-half  to  fifteen  per  cent,  in  excess  of  voids  in  aggregate. 
Plumbs  were  used  in  the  clam  to  within  fifteen  feet  of  the  top, 
and  above  this  level  iron  tram  rails  were  placed  in  string  courses. 
The  success  accompanying  the  use  of  concrete  in  structures  of 
this  magnitude  is  sufficient  evidence  of  its  value  and  adapta- 
bility. 


1  Mr.  A.  B.  Moncrieff,  Engineer  in  Chief,  Engineering  News,  April  7,  1904. 


488  CEMENT  AND  CONCRETE 

ART.  85.     LOCKS 

767.  The  use  of  concrete  in  the  construction  of  canal  locks 
is  comparatively  recent,  but  it  has  met  with  much  favor,  and 
its  use  is  extending.     The  requirements  for  a  lock  wall  are  that 
it   shall   be   reasonably  water-tight,  that  its   strength   shall   be 
sufficient  to  withstand  the  thrust  of  the  gates  and  support  the 
earth  filling  behind  it  (or  in  a  river  wall,  the  difference  in  water 
pressure   on   the   two   sides),   and   that  it   shall   withstand   the 
impact  and  abrading  action  of   boats   using  the  canal.     In  all 
of  these  respects  concrete  is  believed  to  be  the  equal  of  a  good 
class  of  stone  masonry.     At    St.   Marys  Falls  Canal,   portions 
of  the  lock  walls  which  have  been  injured  by  boats  and  re- 
paired with  concrete  have  given  entire  satisfaction,   although 
in  such  cases  the  concrete  had  to  be  patched  on,  and  some- 
times in  places  difficult  of  access  for  work  of  this  character. 

768.  Methods  of  Building.  —  The  present  accepted  method 
of  concrete  lock  construction  is  to  build  the  walls  in  alternate 
sections,   filling  in   the  intermediate  sections   after  the  others 
have   set.     It   is    sometimes    thought   necessary   to    make    the 
work  on  a  section  continuous  from  time  of  starting  the  con- 
creting to  its  completion.     That  the  exterior  appearance  of  the 
work  may  be  somewhat  better  if  such  a  course  is  followed,  is 
true,  but  it  is  very  questionable  whether  the  attainment  of  this 
desirable  result  is  worth  the  additional  expense  and  the  addi- 
tional liability  of  having  poor  work  done  under  the  cover  of 
darkness  when  work  at  night  is  necessitated  by  such  a  rule. 
With   proper   precautions,    such   as   making   steps   in   the   top 
surface  of  work  left  for  the  night,  as  already  detailed  elsewhere, 
and  being  careful  that  the  limit  of  work  on  exposed  faces  is 
bounded   by   true   horizontal   and   vertical  lines,   the   plane   of 
weakness  occasioned  by  a  horizontal  joint  extending  only  par- 
tially through  the  work   cannot    be  a  serious  defect  in  a  con- 
crete wall. 

769.  The  molds,  so  far  as  the  walls  alone  are  concerned,  are 
comparatively  simple  and  have  already  been  described  under 
the  head   of  forms   (Art.   62).     Cable   passages,   gate  recesses, 
hollow  quoins,   culverts,  etc.,   call  for  special  carpentry  work, 
sometimes  of  quite  intricate  character.     While  the  efficiency  of 
the  machinery  and  the  lock  as  a  whole  should  not  be  sacrificed 


LOCKS  489 

to  obtain  easy  construction,  yet  sharp  corners  should  always 
be  avoided,  and  simplicity  of  outline  should  be  the  constant 
aim.  Linings  of  hollow  quoins  (when  steel  quoins  are  consid- 
ered necessary),  gate  anchorages,  cable  sheaves  and  other  parts 
built  into  the  masonry,  are  in  general  placed  with  greater 
difficulty  in  concrete  forms  than  in  stone  masonry.  Aside  from 
such  special  constructions,  the  walls  may  be  built  up  much 
more  rapidly  of  concrete  than  of  stonework. 

As  to  the  proportions  to  be  used  in  concrete  for  locks  there 
is  no  rule  of  thumb.  As  a  guide,  the  stresses  in  each  part  of 
the  structure  should  be  determined  as  well  as  the  knowledge  of 
the  forces  will  permit,  but  the  proportions  will  depend  on  the 
question  of  water-tightness  and  freedom  from  deterioration  quite 
as  much  as  upon  required  strength.  It  may  be  said,  however, 
that  in  a  considerable  portion  of  the  cross-section  of  the  walls, 
weight  is  the  main  consideration  and  the  concrete  need  not  be 
very  rich.  The  concrete  surrounding  the  culvert,  however, 
should  be  of  good  quality,  as  the  stresses  which  may  be  devel- 
oped here  do  not  admit  of  close  analysis. 

770.  The  walls  should  be  faced  with  mortar  made  of  one 
and  one-half  or  two  parts  sand,  or,  better,  two  parts  of  granite 
screenings  one-half  inch  and  smaller,  to  one  part  of  the  same 
kind  of  cement  used  in  the  body  of  the  concrete.  This  facing 
need  not  be  more  than  three  inches  thick,  and  if  made  of  sand 
and  cement,  it  will  probably  be  better  if  not  more  than  one  inch 
thick,  though  this  may  depend  on  the  materials  and  local  con- 
ditions. In  any  case  this  facing  should  be  laid  with  the  con- 
crete by  means  of  a  removable  steel  plate  similar  to  that  de- 
scribed in  §  528.  The  top  of  the  wall  should  be  finished  with 
mortar  or  granolithic  similar  to  a  concrete  walk  or  driveway. 
While  the  walls  should  in  general  have  a  vertical  face,  a  slight 
batter  is  allowable  at  the  top,  starting  at  about  upper  pool  level, 
to  protect  the  concrete  from  being  chipped  by  the  impact  of 
boats,  and  for  a  similar  purpose  the  outer  corner  of  the  wall 
should  be  rounded  with  six  to  twelve  inch  radius. 

Special  care  must  be  taken  in  lining  the  culverts,  particularly 
in  silt-bearing  streams,  and  in  such  places  as  a  change  is  made 
in  the  direction  of  the  flowing  water.  For  high  heads  it  may 
be  necessary  to  line  the  culverts  with  cast  iron  for  a  portion  of 
their  length.  Granite  and  hard  burned  bricks  have  also  been 


490  CEMENT  AND  CONCRETE 

used  for  this  purpose,  but  in  locks  of  moderate  lift,  granolithic 
lining  will  usually  be  found  sufficiently  resistant. 

All  necessary  irons  and  bolts  should  be  built  into  the  masonry 
as  the  work  progresses,  as  they  will  be  much  more  secure  than 
if  set  later  in  recesses  left  for  them. 

771.  Cascades    Lock.  —  The  large  lock  in  the  canal  at  the 
Cascades  of  the  Columbia  was  one  of  the  first  in  the  United 
States  to  be  designed  of  concrete  in  this  country.     In  this  lock 
the  walls,   wells,   copings  and  portions  of  culverts  were  faced 
with  stone.     The  foundation  rock  was  covered  with  eight  inches 
of  rich  concrete,  one  part  Portland  cement,  two  parts  sand  to 
four   parts   gravel.     Fourteen  feet   of   the   chamber   walls   and 
ten  feet  of  gate  abutments  or  wide  walls  were  of  concrete,  one 
to  three  to  six,  while  balance  of  masonry  was  of  one  to  four  to 
eight  concrete. 

The  molds  were  of  four  by  six  posts  four  feet  apart,  and 
lagging  of  two-inch  lumber,  dressed  to  size  for  exposed  faces. 
The  work  was  carried  up  in  horizontal  layers,  not  more  than 
two  feet  being  placed  in  one  day.  The  set  concrete  was  picked 
and  washed  when  fresh  concrete  was  to  be  laid  upon  it  so  as  to 
get  as  good  a  bond  as  possible.  The  inlet  pipes  to  the  turbines 
to  operate  the  machinery  were  built  in  the  lock  walls,  and  as  it 
was  not  desirable  to  place  an  iron  pipe  in  this  location,  the  pipe 
was  molded  of  concrete  and  afterwards  laid  in  the  wall.  The 
pipe  was  thirty-nine  inches  diameter,  walls  six  inches  thick  and 
contained  about  0.22  cubic  yard  of  concrete  per  foot.  It  was 
made  in  three  foot  lengths  in  vertical  molds,  and  the  cost  of 
about  six  hundred  feet  of  it  was  at  the  rate  of  $3.56  per  foot, 
or  $16.19  per  cubic  yard. 

772.  Hennepin   Canal.  —  In  the  locks  for  the  Illinois  and 
Mississippi  Canal  the  walls  are  entirely  of  concrete,  and  were 
built  in  alternate  sections  about  thirty  feet  long.     Work  on  a 
given   section   once   commenced   was   continued   to   completion 
without  intermission.     The  top  was  finished  without  any  plas- 
ter or  wet  coat,  the  excess  concrete  being  simply  cut  off  with 
a   straight   edge   and   rubbed   smooth   and   hard   with   a   float. 
Vertical  wells  one  foot  square  were  left  in  the  walls  at  intervals, 
and  these  were  kept  filled  with  water  for  about  three  weeks 
after  the  completion  of  the  section,  and  then  filled  with  concrete. 
To  avoid  weak  places  due  to  single  batches  made  from  cement 


LOCKS  491 

of  poor  quality  which  might  have  passed  inspection,  the  ce- 
ment was  mixed  in  lots  of  five  to  ten  barrels  before  being  used 
in  the  concrete. 

The  quoins  of  these  locks  were  of  cast  iron.  The  founda- 
tions and  the  spaces  in  rear  of  lock  walls  are  cut  off  from  upper 
pool  by  cross-walls,  and  are  underdrained  to  the  lower  pool  to 
prevent  the  action  of  water  pressure  due  to  the  upper  pool 
level  tending  to  force  up  the  foundation.  Ten  inch  and  twelve 
inch  tile  drains  were  used  for  this  purpose. 

The  proportions  used  in  general  were  one  part  Portland 
coment,  three  to  three  and  one-third  parts  gravel,  and  four 
parts  broken  stone,  the  concrete  containing  about  one  and  four- 
tenths  barrels  of  cement  per  yard.  The  average  cost  of  con- 
crete in  quantities  of  two  thousand  to  four  thousand  yards  was 
from  $8.50  to  $9.15  per  cubic  yard,  distributed  approximately 
as  follows:  — 

Materials $5.00  to  $6.00 

Molds 82  to    1.42 

Mixing  and  placing 1 .64  to    1 .82 

Miscellaneous .12to      .47 

773.  Herr  Island.  —  In  the  Herr  Island  Locks,  Alleghany 
River,  the  failure  of  the  cofferdam  to  exclude  water  from  the 
lock  pit  on  account  of  porosity  of  the  river  bed,  led  to  the  adop- 
tion of  a  concrete  foundation,  laid  "under  water,  of  sufficient 
weight  to  balance  the  hydrostatic  pressure.  After  this  founda- 
tion was  in  place,  the  cofferdam  was  pumped  out  and  the  con- 
crete side  walls  built  in  the  dry. 

The  concrete  was  placed  in  one  foot  courses  covering  the 
entire  area  of  the  wall,  the  forms  being  made  of  one  course  of 
two  by  twelve  inch  plank  set  on  edge  and  halved  at  the  ends 
to  form  two  inch  lap  splices.  Iron  rods  one-quarter  inch  diam- 
eter were  placed  six  feet  eight  inches  apart  to  tie  face  and 
back  plank  together.  A  two  by  twelve  inch  cross-plank  was 
placed  on  edge  beside  each  tie  rod,  dividing  the  work  into  short 
sections.  After  completing  the  concreting  to  the  top  of  the 
forms  throughout,  the  cross-planks  were  removed  and  the  space 
filled  with  concrete,  thus  making  a  vertical  joint.  The  forms 
for  the  next  course  were  then  put  in  place  in  a  similar  manner. 
The  size  of  stone  used  as  aggregate  was  first  two  inches  in  one 
dimension,  but  this  size  was  afterward  reduced  to  one  and 


492  CEMENT  AND  CONCRETE 

one-half  inches,  and  finally  to  one  inch,  the  smaller  size  stone 
being  preferred. 

774.  Mississippi  River.  —  The  lock  in  the  Mississippi  River 
between  Minneapolis  and  St.  Paul  was  founded  on  a  soft  sand- 
stone  rock  having  many  water-bearing  seams.     The  lock  was 
surrounded   on  three  sides  by   a   cut-off  wall.     A  trench  two 
inches  wide  and  ten  feet  deep  was  cut  in  the  soft  rock  by  jet- 
ting a  series  of  holes  in  close  juxtaposition  and  then  breaking 
out  the  intervening  wall  with  a  drill  and  saw  of  special  con- 
struction.    In  this  trench  was  first  laid  a  double  thickness  of 
three-quarter  inch  boards  and  the  remaining  space  was  grouted 
full.     Sections   of   this  wall   afterward   uncovered,  showed   the 
method  to  have  been  very  effective.     Similar  methods  of  seal- 
ing open  seams  in  rock  by  the  use  of  grout  under  pressures 
have  been  used  elsewhere. 

The  forms  for  the  construction  of  this  lock  were  of  excellent 
design1  and  have  been  described  under  the  head  of  "forms" 
(§  514).  The  walls  were  built  in  alternate  blocks,  twelve  feet 
long.  At  the  ends  of  the  blocks  are  left  vertical  spaces  five  by 
seven  inches,  to  be  filled  with  mortar  and  other  water-tight 
composition.  The  forms  are  lined  with  sheet  iron,  and  to 
obtain  a  smooth  face  the  concrete  is  thrown  against  the  lining, 
the  stones  rebound,  leaving  only  mortar  on  the  face.  The 
face  is  rammed  with  tampers  of  special  form,  wedge  shaped, 
and  measuring  }  inch  by  5  inches  on  the  lower  edge.  This  is 
followed  by  a  flat  rammer.  The  finish  is  said  to  be  excellent. 

775.  Sand-cement  was  used   quite  largely  in   the  lock   con- 
struction.    It  was  prepared  at  the  site  of  the  work,  of  equal 
parts  Portland  cement  and  siliceous  sand  ground  together  in  a 
tube  mill. 

Proportions  in  the  concrete  were  varied  somewhat  from  time 
to  time,  though  in  general  it  was  mixed  one  part  silica  cement, 
two  and  one-third  parts  sand  and  six  and  two-thirds  parts  of 
crushed  stone  without  screening.  Tests  showed  that  about  ten 
per  cent,  of  this  crusher  product  was  fine  enough  to  be  consid- 
ered sand,  and  account  of  this  fact  was  taken  in  fixing  the  pro- 
portions as  above.  The  cost  of  the  concrete,  over  11,000  yards, 
was  as  follows :  — 


1  Mr.  A.  O.  Powell,  Asst.  Engr.,  Report  Chief  of  Engrs.,  1900,  p.  2778. 


BREAKWATERS  493 

Cement $2.76 

Stone $1.29 

Breaking  stone  for  crusher .38 

Crushing  stone .82 

Total  stone $2.49 

Sand    ,  .52 


Total  materials  .    .    . 

Forms 

Mixing  and  placing  concrete 


Total  cost  per  cubic  yard  concrete     .  $8.42 

ART.  86.     BREAKWATERS 

776.  The  use  of  concrete  in  the  construction  of  breakwaters 
in  the  United  States  was  suggested  as  early  as  1845.     In  recent 
years   it   has   been   employed   quite  extensively,   especially  for 
harbor  improvements  on   the  Great  Lakes,  where  it  has  with- 
stood the  rigorous  winters,  the  severe  storms,  the  attrition  of 
ice,  and  the  impact  of  boats,  in  a  highly  satisfactory  manner. 
Its  use  has  been  confined  largely  to  the  construction  of  a  super- 
structure on  timber  cribs,  the  concrete  work  being  in  the  form 
of  blocks  set  with  derricks,  or  of  monolithic  blocks  molded  in 
place,  or  more  frequently  composed  of  a  combination  of  these 
two  forms. 

Since  in  breakwater  construction  weight  is  of  prime  impor- 
tance, it  is  not  necessary,  in  general,  to  use  an  exceptionally 
strong  concrete,  as  the  increased  expense  had  better  be  in- 
curred in  increasing  the  cross-section. 

777.  Buffalo  Breakwater.  —  In  the  construction  of  the  ex- 
tensive breakwaters  at  Buffalo,1  concrete  has  been  used  in  large 
quantities  and  according  to  various  plans.     In  1887  the  super- 
structure of  some  750  feet  of  timber-crib  breakwater  was  re- 
newed, mainly  with  natural  cement  concrete.     250  feet  of  this 
superstructure   was   built   with   a   facing   of    Portland    cement 
concrete,  while  500  feet  of  it  was  faced  with  stone  masonry. 
The   concrete  started   two  feet  below   mean   lake  level.     The 
cross-section  of  the  superstructure  was  about  350  square  feet, 
and  the  cost  of  concrete,  exclusive  of  materials,  was  about  $2.36 
per  cubic  yard. 


1  Described  by  Mr.  Emile  Low,  U.  S.  Asst.  Engr.     Trans.  Am.  Soc.  C.  E., 
December,  1903. 


494  CEMENT  AND  CONCRETE 

During  the  following  year  concrete  footing  blocks  were  used 
on  both  the  lake  and  harbor  faces,  since  it  was  found  that  the 
cement  was  washed  out  of  the  concrete  laid  in  place  below 
water.  The  blocks  contained  about  3J  cubic  yards  and  cost  on 
the  average  a  little  more  than  $30.00  each,  or  $37.35  each  in- 
cluding the  setting,  or  at  the  rate  of  $11.29  per  cubic  yard. 
The  molds  or  forms,  which  were  used  repeatedly,  cost  about 
$40.00  each. 

778.  Another  style  of  concrete  superstructure  developed  at 
Buffalo    is    that   recommended    by  Major    F.  W.  Symons.     It 
consists  of  three  longitudinal  walls,  connected  at  intervals  by 
cross-walls,  filled  between  with  rubble  stone  and  provided  with 
heavy  parapet  and  banquette  decks.     The  longitudinal  wall  on 
the  lake  side  is  founded  on  heavy  concrete  blocks  5  feet  high, 
8  feet  thick  at  the  base  and  7.2  feet  long  ;  the  two   minor  walls 
are  formed  by  smaller  blocks,   4  feet  by  4.5  feet  by   12  feet. 
The  total  width  at  base  is  36  feet.     The  space  between  lake  face 
blocks  and  center  row  is  14  feet,  and  between  center  row  and 
harbor  face  blocks  is  about  5  feet.     The  cross-wall  blocks  are 
7  by  6  by  4  feet  under  the  parapet,  and  4  by  3  by  4  feet  under 
the  banquette,  all  spaced  36  feet  centers.     All   concrete  blocks 
have  their  bases  set  two  feet   below  mean  lake  level  and  have 
panels   in  their  upper    surfaces    to  provide  a  bond    with  the 
concrete  laid  in  place. 

The  lake  wall  above  the  concrete  block  is  8  to  4  feet  thick, 
with  batter  on  face,  and  the  decks  are  3  to  4  feet  thick,  built  of 
concrete  in  place.  The  forms  for  the  harbor  face  wall  and  cross- 
walls  were  of  J  inch  matched  pine,  with  vertical  posts  two  to 
three  feet  centers  tied  through  the  wall  with  one-half  inch  tie 
rods. 

The  concrete  was  composed  of  the  following  volumes:  one 
part  Portland  cement,  one  part  screened  gravel  (about  f  inch), 
two  parts  sand  grit  (nearly  half  of  which  was  J  inch  to  \  inch 
gravel),  and  four  parts  unscreened  broken  limestone  (about  11 
per  cent.  dust).  The  cost  of  the  concrete  in  blocks  was  $10.00 
per  cubic  yard,  and  that  in  place  cost  $9.40  per  cubic  yard. 

779.  Cleveland  Breakwater.  —  Several  forms  of  concrete  su- 
perstructure   have  been  employed    in  the  work  at    the  Cleve- 
land breakwater.     One   section  on  a  thirty-two   foot  crib  has 
three  rows  of  concrete  blocks,  one  each  on  lake  and  harbor 


BREAKWATERS  ,  495 

sides  and  one  in  center  of  the  crib,  extending  three  feet  below 
mean  lake  level.  The  concrete  in  place  is  started  at  mean  lake 
level  and  is  composed  of  a  base  five  feet  thick,  with  vertical 
faces  over  the  entire  crib,  and  surmounted  on  the  lake  side  by 
a  parapet  five  feet  high  and  about  twelve  feet  wide.  The  stone 
filling  of  the  cribs  was  covered  with  a  cheap  decking  of  wood 
before  laying  the  concrete  in  place. 

780.  Marquette   Breakwater.  —  In    the   construction   of   the 
superstructure  of  the  breakwater  at  Marquette,  Mich.,  the  con- 
ditions were  peculiar  in  that  it  was  desirable  to  provide  a  pas- 
sageway within  the  superstructure  through  which  the  lighthouse 
on  the  outer  end  might  be  reached  in  stormy  weather.     This 
was  accomplished  by  leaving  near  the  harbor  face  a  conduit, 
6  feet  3  inches  high  and  2  feet  10  inches  wide,  the  entire  length 
of  the  structure. 

The  old  timber  structure  having  been  removed  to  about  one 
foot  below  mean  lake  level,  a  foundation  course  two  feet  thick 
of  Portland  cement  concrete  was  laid  on  a  burlap  carpet  placed 
over  the  stone  filling  of  the  crib.  Upon  this  the  monolithic 
blocks  were  built  in  place,  substantial  molds  being  set  up  for 
alternate  blocks  ten  feet  apart.  After  these  had  set,  the  molds 
were  removed  and  other  molds  set  up  to  form  the  two  faces  of 
the  intervening  blocks,  the  ends  of  the  blocks  already  com- 
pleted taking  the  place  of  end  molds.  The  monolithic  blocks 
were  of  natural  cement  concrete  in  proportions  of  489  pounds 
of  cement  to  one-half  cubic  yard  of  sand  and  one  cubic  yard  of 
broken  stone.  About  twenty  per  cent,  of  these  monoliths  was 
composed  of  rubble  stone  ranging  in  size  from  one-half  to  three 
cubic  feet,  care  being  taken  that  no  rubble  should  be  placed 
nearer  than  one  foot  to  any  outside  surface.  The  standard 
block  was  twenty-three  feet  wide  on  the  base,  which  was  one 
foot  above  mean  lake  level.  The  lower  five  feet  of  the  face  had 
a  45°  slope.  There  was  then  a  nearly  level  berm,  7.5  feet  wide, 
forming  the  banquette  deck;  from  the  back  of  this  deck  the 
face  sloped  at  an  angle  of  45°  to  the  parapet  deck,  which  was 
6  ft.  4  inches  wide.  The  harbor  side  of  the  block  was  vertical, 
9.4  feet  high.  Since  the  structure  proved  very  stable  and  free 
from  vibrations  in  heavy  seas,  the  horizontal  dimensions  of  the 
block  were  reduced  as  the  shore  was  approached. 

781.  The  method  of  placing  the  Portland  cement  concrete 


496  CEMENT  AND  CONCRETE 

foundation  was  modified  as  described  under  the  head  of  the 
block  and  bag  systems  of  concrete  constructions  (Art.  64). 

The  cost  of  the  monolithic  blocks  of  natural  cement  concrete 
was  as  follows :  — 

490  Ibs.  cement,  $1.04  per  bbl $1.815 

.5  cu.  yd.  sand,  $0.50  per  cu.  yd .25 

1.0  cu.  yd.  stone,  $1.58    "     "      " 1.58 

Materials  in  one  cubic  yard  concrete $3.645 

80  per  cent,  concrete  in  the  finished  block,  .80  of 

$3.645      $2.91 

Loading  materials .33 

Mixing  concrete .52 

Depositing  concrete .41 

Handling  rubble .09 

Finishing  blocks .09 

Moving  and  setting  forms .25 

Timber  waling,  anchor  boJts,  etc .13 

Total  cost  in  place  per  cu.  yd $4.73 

Very  interesting  and  detailed  accounts  of  the  construction 
of  this  breakwater,  which  was  carried  out  with  special  care  as 
to  all  details,  were  made  by  Mr.  Clarence  Colenlan,  Asst.  Engr., 
and  may  be  found  in  the  reports  of  Major  Clinton  B.  Sears, 
Reports  Chief  of  Engineers,  U.  S.  A.,  1896  and  1897. 


INDEX 


Abrasion  — 

Resistance  to,  329. 
Tests  of,  94. 
Abutments,  467. 

Accelerated  Tests  (see  Soundness),  77. 
Acceptance  of  Cement,  153. 
Accuracy  Obtainable  in  Tests,  137. 
Acid- 

Sulphuric,  in  Cement,  34. 
Use  on  Concrete  Surface,  368. 
Adhesion  — 

Cement  to  Brick,  273,  278. 
Glass,  273. 
Iron,  273. 
Steel  Rods,  284. 
Stone,  272. 
Terra  Cotta,  273. 
Effect  of  Character  Surface,  276. 
Plaster  Paris,  277. 
Regaging,  276. 
Richness  Mortar,  274. 
Neat  and  Sand  Mortars,  279. 
Portland  to  Natural,  270. 
Results  of  Tests,.  270. 
Tests  of  Cement,  92. 
Adulteration,  4,  43. 
Age  and  Aeration  of  Cement  — 
Effect  on  Time  Setting,  68. 

Specific  Gravity,  42. 
Strength,  235. 
Aggregate  — 

Bowlder  Stone,  322. 
Brick,  186,  324,  335. 
Cinders,  302,  309,  338. 
Clean,  188. 
Cost,  195. 
Crushing,  194. 
Fireproof  Concrete,  335. 


Aggregate  — 

Granite,  322. 

Gravel  as,  192,  298,  303,  309. 

Material  for,  186. 

Sand  in,  202. 

Sandstone,  294,  322. 

Sea  Water,  350. 

Size  and  Shape  of  Fragments,  188. 

Tests  of,  298,  322. 

Trap,  298,  309. 

Voids  in,  190. 

Weight  of,  189. 
Air  Hardened  Mortars,  122,  232. 

260. 

Alum  and  Soap  Washes,  344. 
Alumina  in  Cement,  33. 
Aluminous  Natural  Cement,  25. 
Amount  of  Mortar  in  Concrete,  200. 

Effect  on  Compressive  Strength, 
293. 

Effect  on  Transverse  Strength, 

318. 
Analysis  — 

Methods,  35. 

Materials,  11. 

Natural  Cement,  8. 

Portland  Cement,  6. 
Anchor  Bolts,  284,  471. 
Arch- 

Big  Muddy  River,  481. 

Highway,  480. 

Mechanicsville,  480. 

Melan,  384,  483. 

Monier,  382. 

Plain  Concrete,  480,  481. 

San  Leandro,  480. 

Thacher,  385. 

Three  Span,  480. 


497 


498 


INDEX 


Arch  — 

Topeka,  Kan.,  483. 

Wiinsch,  383. 
Arches  — 

Centers,  478,  482. 

Construction,  478. 

Cost,  483. 

Design,  474. 

Drainage,  479. 

Finish,  479. 

Viaduct,  484. 

Bag    for    Depositing    Concrete,    369, 

373,  377. 

Bag  Method,  374. 
Bags  of  Concrete  to  Form  Face,  377. 

-     to  Prevent  Scour,  377. 
Baker,  Classification  of 

Hydraulic  Products,  3. 
Ball  Mills  for  Grinding,  20. 
Barrels,  Cement  — 

Capacity,  172. 

Records,  146. 
Basement  Floors,  426. 
Base  of  Concrete  Walk,  421. 
Beams  — 

Concrete-Steel,  390. 

for  Street  Railway  Tracks,  433. 

Steel,  Protected,  412. 

Strength,  Experiments,  313,  403. 
Formulas  for,  391,  393. 
Tables  of,  400,  402. 
Belt  Conveyor  for  Concrete,  358. 
Blast  Furnace  Slag  — 

Cement,  22,  23. 

Sand,  159. 

Block  System,  351,  378. 
Blocks,    Concrete,    in     Breakwaters, 

379,  493. 

Blowing  of  Cement  (see  Soundness). 
Board,  Mixing,  for  Concrete,  204. 
Bohme  Hammer  Apparatus,  114. 
Boiling  Test,  77. 

Bolts,  Adhesion  of  Mortar  to,  284. 
Boston  Elev.   R.R.   Tests  Concrete, 

292,  308. 
Boston  Subway,  444,  446. 


Bowlder  Stone  as  Aggregate,  322. 
Box  Mixer  (see  Cubical). 
Braces  for  Forms,  354. 
Breaking  Briquets,  123. 
Breaking  Stone  by  Hand,  194. 
Breakwater,  493. 

Buffalo,  214,  493. 
Cleveland,  494. 
Concrete  in,  379,  493. 
Marquette,  375,  379,  495. 
Brick  - 

Adhesion  of  Cement  to,  272. 
as  Concrete  Aggregate,  186,  324, 

335. 

Dust  with  Cement,  258. 
Bridge  — 

Abutments,  467. 
Piers,  464. 

Forms  for,  464. 
Bridges  (see  Arches). 
Briquets  — 

Area  Breaking  Section,  109. 
Breaking,  123. 
Form  of,  108. 
Machine  for  Making,  1 14. 
Methods  of  Making,  113. 
Records,  147. 
Storing,  117. 
Broken  Stone  (see  Aggregate). 

vs.  Gravel,  192. 

Brushing  Concrete  Surface,  361,  366. 
Buffalo  Breakwater,  214,  493. 
Buffalo,  Concrete  Mixing  at,  214. 
Buhr  Millstones,  20. 
Building  Regulations,  New  York,  418. 
Buildings  of  Concrete,  410. 
Burlap   Bags   for   Placing   Concrete, 

369,  377. 
Burning  — 

Natural  Cement,  26. 
Portland  Cement,  16. 
Bushhammering  Concrete,  367. 

Caisson  Filling,  466. 
Calcium  Chloride  — 

Effect  on  Setting,  70. 

Test  for  Soundness,  81. 


INDEX 


499 


Calcium  Sulphate  — 

Effect  on  Strength,  249. 

Time  Setting,  69. 
Canal  Locks  — 

Concrete  for,  224,  357,  488. 

Forms  for,  357. 

Capacity  Cement  Barrels,  172. 
Carbonic  Acid,  34. 
Cars  — 

Concrete  Plant  on,  216. 

for  Transporting  Concrete,  213. 
Cascades  Canal,  Concrete  for,  224. 
Centers  (see  also  Forms)  — 

for  Arches,  478,  480. 

for  Tunnel  Lining,  451. 
Chamber  Kilns,  17. 
Chemical  Tests,  31. 
Chicago  Drainage  Canal,  Concrete  on, 

224. 
Cinder  Concrete  — 

Strength,  302. 

Modulus  Elasticity,  309. 
Cinders,  Sulphur  in,  338. 
Classification  Hydraulic  Products,  1. 
Clay- 

for  Cement  Manufacture,  10. 

in  Concrete,  305. 

in  Mortar,  253. 
Clip  for  Breaking  Briquets,  124. 

Cock,  128. 

Form  Suggested,  133. 

Gimbal,  130. 

Requirements  for  Perfect,  132. 

Russell,  129. 

Tests  of,  131. 
Clip  Breaks,  126. 

Cause,  126. 

Prevention,  127. 

Strength,  127. 

Coarse  Cement  and  Fine  Sand  Com- 
pared, 57,  62. 
Coarse  Particles  (see  Fineness)  — 

Effect  of,  52. 

on  Time  Setting,  69. 
Cock  Clip,  128. 

Cockburn  Concrete  Mixer,  211. 
Coefficient  Expansion,  332. 


Cohesion    and   Adhesion    Compared, 

275,  279. 

Cold,  Effect  on  Cement,  260. 
Color  for  Concrete  Finish,  367. 
of  Cement,  36. 

of  Concrete  Surface,  365,  367. 
Columns,  412,  415. 

Concrete-Steel,  413. 

Steel,  Filled  and  Covered,  413. 

Strength  of,  413. 
Comparative  Tests  — 

Natural  Cements,  138. 

Portland  Cements,  138. 
Compression  Tests,  89. 
Compressive  Strength  — 

Concrete,  291. 

Mortar,  288. 
Compressive    and    Tensile    Strength 

Compared,  288,  313. 
Compressive  and  Transverse  Strength 

Compared,  313. 
Composition,  Chemical,  6,  8. 

Effect  on  Specific  Gravity,  42. 
Concrete  — 

Amount  of  Mortar  in,  200. 

Compressive  Strength  of,  291. 

Construction,  Rules  for,  467. 

Cost,  218. 

Definition,  186,  200. 

Deposition  in  Water,  326,  369. 

Making,  200. 

Mixers,  207,  212. 

Mixing,  Cost,  212. 

Mixing  by  Hand,  203. 

Mixing  Plants,  212. 

Proportions  in,  200. 

Thorough  Mixing,  203. 
Concrete-Steel,  381. 
Conductivity  of  Concrete,  333. 
Considered  Experiments,  388. 
Consistency     Concrete,      Effect     on 

Strength,  293,  296,  319. 
Consistency  Mortar,,  176. 

Determination,  97. 

Effect  on  Adhesion,  274. 

Tensile    Strength,    99, 
232,  314. 


500 


INDEX 


Consistency  Mortar  — 

Effect  on  Time  Setting,  71. 

Transverse  and  Compressive 

Strength,  314. 

Effect  in  Low  Temperatures,  268. 
Constancy  of  Volume  (see  Soundness) . 
Contraction  Concrete  in  Setting,  331. 
Coosa  River  Concrete  Plant,  212. 
Coping  for  Retaining  Wall,  467. 
Corners  of  Concrete  Forms,  354. 
Corrosion,  Action  of,  336. 
Cost  — 

Aggregate,  195. 
Concrete,  218. 
Arch,  483. 

Curb  and  Gutter,  432. 
Floor,  427. 
Mixing,  212. 
Tunnel  Lining,  452. 
Walk,  425,  426. 
Mortar,  182. 
Sand,  171. 
Sand  Washing,  170. 
Cracks  in  Concrete,  361. 
Crushing  Strength  (see  Compression). 
Cubes,  Concrete,  Tests  of,  292. 
Cubical  Concrete  Mixer,  208,  212. 
Curb  and  Gutter,  431. 
Cut  Stone  Facing,  477. 
Finish,  366. 
Cylinder,  Steel,  Bridge  Pier,  465. 


Dams,  484. 

Barossa,  487. 

Butte,  486. 

Concrete  vs.  Rubble,  484. 

Massena,  486. 

San  Mateo,  487. 

St.  Croix,  486. 
Definitions,  1. 
Delivery  of  Cement,  144. 
Density,  Apparent,  37. 
Deposition     Concrete     in     Running 

Water,  326,  369. 
Deterioration  of  Cement,  235. 
Deval,  Test  for  Soundness,  78,  81 . 


Diary,  Use  of,  153. 

Dietsch  Kiln,  ]  7. 

Drake  Concrete  Mixer,  211,  216. 

Dromedary  Concrete  Mixer,  209. 

Efflorescence,  346. 
Estimates,  Cost  Concrete,  218. 

Mortar,  182. 

Excessive  Reinforcement,  396. 
Expanded  Metal,  387. 
Expansion  — 

Coefficient  of,  332. 

Concrete  in  Water,  331. 

Joints,  482,  484. 
Experiments  — 

Columns,  413. 

Concrete-Steel,  388,  397,  403. 

Considered,  388. 

Hooped  Concrete,  414. 

Face  of  Concrete  (see  also  Finish)  — 

Bushhammer,  367. 

Colors  for,  365. 

Cut  Stone,  366,  477. 

Efflorescence,  346. 

Lock  Walls,  489. 

Mortar,  363. 

Pointed  or  Tooled,  367. 
Face  Pressed  in  Compressive  Tests, 

292. 
Faija,  Mortar  Mixer,  107. 

Tests  for  Soundness,  78. 
Failure  of  Concrete  in  Sea  Water,  348. 
Farrel's  Wall  Molds,  417. 
Filtration  through  Concrete,  340,  342. 
Fineness  Cement  — 

Effect  on  Specific  Gravity,  52,  59. 
Strength,  54,  60. 
Time  Setting,  52,  60,69. 
Weight,  59. 

Importance,  45. 

Specifications,  51. 

Tests,  45. 
Fineness  of  Sand,  97. 

in  Freezing  Weather,  268. 
Finish  of  Concrete  Surface,  363. 

Colors,  367. 


INDEX 


501 


Finish  of  Concrete  Surface  — 
Mortar,  363. 
Pebble-dash,  366. 
Plaster  Paris,  365. 
Rubbed,  365. 
Shovel,  363. 
Tooled  or  Pointed,  367. 
Fire,  Resistance  Concrete  to,  332. 
Fireproof  Buildings,  332. 
Fireproof  Concrete,  Aggregate  for, 335. 
Flexure,  Concrete-Steel   Beams,   390. 
Tests  Concrete,  314. 

Mortar,  90,  313. 
Floor,  Systems  of  Concrete-Steel,  381 , 

411. 
Floors  — 

Basement,  426. 
Buildings,  411. 
Reservoirs,  453. 
Fonns,  Concrete,  351. 

for  Buildings,  416,  417. 
Bridge  Piers,  464. 
Columns,  416. 
Lock  Walls,  488,  492. 
Piles,  473. 

Reservoir  Roofs,  455. 
Subways,  445,  448. 
Tunnel  Lining,  447,  449,  451. 
Oiling,  354. 
Time  Left  in  Place,  352,  439,  471, 

478. 
Formulas  for  Concrete-Steel  Beams, 

391,  393. 
Foundation  — 

Concrete  Walks,  420. 
Pavements,  428. 
Piles,  471. 

Free  Lime  in  Cement,  31,  76,  83. 
Freezing  Weather  — 

Use  of  Cement  Mortar  in,  260. 
Use  of  Concrete  in,  326. 

Gage  of  Wire  for  Sieves,  46,  47. 
Gaging  Mortar  — 

by  Hand,  105. 

Effect  of  Thorough,  236. 

with  Hoe  and  Box,  106. 


Gaging  Concrete  (see  Mixing). 

German  Normal  Sand,  96. 

Gilmore  Wires  for  Time  Setting,  66. 

Gimbal  Clip,  130. 

Glass,  Adhesion  of  Cement  to,  274. 

Granite  as  Aggregate,  322. 

Granolithic,  Facing,  365. 

Top  Dressing,  422. 
Granulometric  Composition  — 

Aggregate,  189. 

Sand,  163. 
Gravel  as  Aggregate,   186,   192,  298, 

303,  309. 

vs.  Broken  Stone,  192. 
Gravity  Concrete  Mixer,  212. 
Griffin  Mill,  21. 

Grinding  Cement  (see  Fineness),  20. 
Grout,  to  Seal  Cracks,  492. 

on  Surface  Concrete,  363,  365. 
Gutters  and  Curbs,  431. 
Gypsum  (see  Plaster  Paris). 

Hammer,  Bohme,  114. 
Heat,  Effect  on  Concrete,  332. 
Heating  Materials  in  Cold  Weather, 

267,  452. 

Hennebique  System,  385,  409. 
History,  Hydraulic  Products,  1. 
Hoe  and  Box  for  Mortar  Mixing,  106. 
Hoffman  Kiln,  17. 
Hooped  Concrete,  414. 
Hot  Materials  in  Cold  Weather,  267. 
Hot  Tests  (see  Soundness). 
House  Walls,  417. 
Hydraulic  Limes,  2. 


Immersion  of  Briquets,  119. 

Impervious  Concrete,  340,  343. 

"  Improved "  Cement,     Strength    of, 

244. 

Impurities  in  Sand,  168. 
Ingredients  — 

in  Cubic  Yard  Concrete,  218. 

Mortar,  179. 
Portland  Cement,  5. 
Interpretation  Tensile  Tests,  137. 


502 


INDEX 


Iron  — 

Adhesion  Cement  to,  274,  284. 

Corrosion  in  Concrete,  336. 
Iron  Oxide,  33. 

Jig  for  Mortar  Mixing,  107. 
Johnson  Bar,  387. 
Joints  — 

Expansion,  482,  484. 
in  Concrete,  361. 
Blocks,  378. 
Dam,  485. 
Molds,  354. 
Walks,  423,  424. 

Kahn  System,  386,  409. 
Kilns,  Cement,  16. 
Output,  19. 

Lagging  for  Forms,  352. 

Tongue  and  Groove,  352. 
Laitance,  370. 
Lamp  Black,  in  Concrete,  365,  367. 

Surface  Finish,  368. 
Laying  Fresh  Concrete  on  Set  Con- 
crete, 361. 
Le  Chatelier,  Apparatus  for  Specific 

Gravity  Test,  40. 
Test  for  Soundness,  81. 

Time  Setting,  66. 
Lime,  Classification,  3. 

Hydraulic,  3. 
Lime  in  Cement,  31,  245. 
Lime  Paste,  Effect  on  Adhesion,  280. 
Lime,  Slaked,  with  Cement,  245,  345. 
Limestone,  Adhesion  Cement  to,  274, 

277. 
Limestone,    Crushed    as    Aggregate, 

297,  322,  335. 
Limestone  Dust  with  Cement,    160, 

187,  258,  325. 
Lining  of  Forms,  353. 

Reservoirs,  455. 
Loam  in  Sand,  168. 
Lock- 

Cascades,  490. 
Hennepin  Canal,  490. 


Lock  — 

Heir  Island,  491. 

Mississippi  River,  492. 
Locks,  488. 

Culvert  Lining,  489. 

Facing,  489. 

Methods  Building,  488. 

Molds,  488,  490. 

Louisville  and  Portland  Canal,  Con- 
crete on,  223. 

Machine     for     Breaking     Briquets, 
123. 

Concrete  Mixing,  207. 
Mortar  Mixing,  107,  178. 
Maclay,  Test  for  Soundness,  78. 
Magnesia  in  Cement,  32. 
Magnesian  Natural  Cements,  24. 
Manufacture  Natural  Cement,  24. 
Portland  Cement,  10. 
Marking  Briquets,  117. 
Materials  — 

for  Cubic  Yard  Concrete,  218. 

Mortar,  179. 

Natural    Cement    Manufac- 
ture, 24. 

Portland  Cement  Manufac- 
ture, 10. 
Melan  System,  384. 

Arch,  Topeka,  483. 
Microscopical  Tests,  36. 
Mills  - 

Ball,  20. 
Griffin,  21. 
Tube,  20. 

Mixing  Concrete  — 
by  Hand,  204. 

Cost,  206. 
by  Machine,  207. 

Cost,  212. 

Necessity  of  Thorough,  303,  319. 
Mixing  Mortar  — 
for  Tests,  105. 

Use,  177. 

Necessity  of  Thorough,  236. 
Mixing  Natural  and  Portland  Cement, 
243. 


L\'J)KX 


Modulus  of  Elasticity  — 

Concrete,  308. 

Mortar,  306. 
Modulus  of  Rupture  in  Flexure  — 

Concrete  Prisms,  314. 

Mortar  Prisms,  313. 
Moist  Closet  for  Briquets,  119. 
Moistening  Concrete,  362. 
Moisture,    Effect    on   Volume    Sand, 

166. 

Mulder's  iN-rord,  1  17. 
Molding  — 

Bolnne,  Hammer,  114. 

Hand,  115. 

Jamieson  Machine,  114. 

Machine,  114. 

Methods,  113. 
Molds  - 

Briquet,  Cleaning,  113. 
Forms  of.  108. 
Kinds  of,  112. 

Concrete  (see  Forms). 
Blocks,  378. 
Sewers,  439,  442. 
Walks,  422. 
Walls,  417. 

Monier  Arch,  Test,  382. 
Monier  System,  381. 
Mortar  — 

Amount  in  Concrete,  200. 

Cost,  182. 

Definition  of,  155. 

Facing,  363. 

for  Plastering  Concrete,  363. 

Ingredients  for  Cubic  Yard,  179. 

Mixing,  105,  177. 

Varying  Richness,  227. 

Natural  Cement  — 

Analysis,  8. 

Definitions,  8. 

Manufacture,  24. 
Natural   Cement  Concrete,   Strength 

of,  300. 

Neat  vs.  Sand  Tests,  95. 
Needle  Test  for  Time  Setting,  66. 
Numbering  Briquets,  117. 


Oiling  Forms  or  Molds,  334. 

Painting  Concrete,  368. 
Pan  Mixer  — 

for  Cement,  14. 

Concrete,  210. 

Paper  Sacks  for  Concrete,  377. 
Pat  Test  (see  Soundness). 
Pavement,  Concrete,  429. 
Pavement  Foundation,  128. 
IVbblc-Dash  Finish,  366. 
Permeability  of  Mortars,  .",10,  343. 
Piers,  Bridge,  -Nil. 

Forms  for,  461. 
Piles,  Concrete,  471. 

Protection  by  Concrete,  383. 
Pipe,  Sewer,  in  Concrete,  436. 
Placing  Concrete  under  Water,  326, 

369. 
Placing  Consecutive  Layers  Concrete, 

361 . 

Plant,  Portland  Cement,  14. 
Plants,  Concrete,  212. 
Plaster  Paris  — 

Effect  on  Adhesion,  277. 
Strength,  249. 
Soundness,  250,  251. 
Time  Setting,  69. 
Plastering  Concrete  Surface,  363. 
Platform,  Mixing,  204. 
Plums  in  Concrete,  361,  485,  495. 
Point,  Dressing  Surface  Concrete,  367. 
Pointing  Mortar,  347. 
Porosity  of  Mortars,  340. 
Portland  and  Natural  Compared,  279, 

282. 
Portland  Cement  — 

Composition,  5. 

Definition,  4. 

Manufacture,  10. 
Posts  for  Forms,  354,  356. 
Pot  Cracker  for  Grinding,  26. 
Pozzolana  Cement -(see  Slag  Cement), 

7. 

Pozzolana  with  Cement,  365. 
Preservation  of  Iron  and  Steel,  336. 
Proportions  in  Concrete  — 

Theory  of,  200. 


504 


INDEX 


Proportions  in  Concrete  — 

Effect  on  Strength,  295,  301, 317. 
Modulus  of  Elasticity, 

309. 
Proportions  in  Mortar,  173. 

Effect  on  Strength,  227. 
Puzzolana  (see  Pozzolana). 

Qualities,  Desirable,  in  Cement,  28. 

Rails  Imbedded  in  Concrete,  470. 
Hammers  for  Concrete,  360,  492. 
Hamming  Concrete,  359. 

Effect  on  Strength,  297. 
Ransome  Bars,  284,  386. 

Concrete  Mixer,  209. 
System,  386. 
Rate    of    Applying     Tensile    Stress, 

133. 
Ratio       Compressive       to       Tensile 

Strength,  289. 
Records  of  Tests,  140. 
Regaging  Mortar,  237. 

Effect  on  Adhesion,  276. 
Hegrinding  Cement  (see  Fineness). 
Reinforced   Concrete    (see   Concrete- 
Steel). 

Reinforcement,  Double,  403. 
Excessive,  396. 
Longitudinal,  413. 
Single,  390. 

Repair  of  Stone  Piers,  466. 
Reservoirs,  453. 

Examples,  456. 
Floor,  453. 
Lining,  455. 
Roof,  455. 
Walls,  454. 

Results  of  Tests,  Treatment  of,  135. 
Retaining  Walls,  467. 
Retardation  of  Setting  of  Cement,  69. 
Richness     of     Concrete,     Effect     on 

Strength,  296,  317. 
Rods,  Adhesion  of  Mortar  to,  284. 

Tie,  for  Forms,  356. 
Roebling  System,  386. 
Roman  Cement,  Definition,  2. 


Roof,  Concrete,  for  Building,  411. 

for  Reservoir,  455. 
Rosendale  Cement  (see  Natural). 
Rubbed  Finish  for  Concrete,  365. 
Rubble  Concrete,  360. 
Rubble  vs.  Concrete,  484. 
Rules  for  Concrete  Construction,  467. 
Russell  Clip,  129. 
Rust,  Prevention  of,  336. 

Sacks  of  Concrete,  374,  377. 
Salt,  Effect  on  Mortars,  263. 

Time  Setting,  70. 
Use  in  Freezing  Weather,  260, 

326. 
Sampling,  Method,  145. 

Per  cent,  of  barrels,  144. 
Sand  — 

Character,  154,  157. 
Cost,  171. 
Damp  — 
'  Mortars  Hardened  in,  278. 

Volume  of,  KM). 
Detecting  Impurities  in,  168. 
Fineness,  97,  159. 
for  Tests  - 

Comparison  of,  96. 
Fineness,  97. 
German  Normal,  96. 
Natural,  96. 

for  Use  in  Sea  Water,  159. 
Heating  in  Winter,  452. 
Impurities  in,  168. 
in  Aggregate,  202. 
Quality,  170. 
Shape  and  Hardness  Grains,  155, 

159,  162. 
Slag,  159. 

Varying  Amounts  of,  227. 
Voids  in,  162. 

Measuring,  164. 
vs.  Neat  Tests,  95. 
Washing,  169. 
Weight,  170. 
Sand-Cement  — 

Manufacture,  21. 
Use  in  Locks,  492, 


INDEX 


505 


Sandstone  — 

Adhesion  of  Cement  to,  274. 
as  Aggregate,  294,  322. 
Sawdust  in  Mortar,  359. 
Screenings    hi     Broken    Stone,    187, 

325. 

Screw  Concrete  Mixer,  211. 
Sea  Wall,  Concrete  in,  216. 
Sea  Water  — 

Cements  in,  348. 
Concrete  in,  318. 
Storing  Briquets  in,  121. 
Section,  Breaking,  of  Briquets    109. 
Setting,  Process  of,  65. 
Setting,  Rate  or  Time  of,  66. 

Approximate  Method  Determ  n- 

ing,  67. 

Effect  of  Aeration,  68. 
Age,  68. 

Composition,  67. 
Consistency,  71. 
Fineness,  69. 
Gaging,  73. 
Gypsum,  69. 
Medium,  74. 
Plaster  Paris,  69. 
Salt  and  Sugar,  70,  71. 
Temperature,  72,  73. 
Gilmore  Wires,  66. 
in  Air  and  Water,  74. 
Mortar  and  Neat  Cement,  72. 
Requirements  as  to,  74. 
Variations  in,  67. 
Vicat  Needle,  66. 
Sewers  — 

Cost,  437,  439. 
Forms,  439,  441. 

Steel,  442. 

Methods  Construction,  436,  443. 
Pipe,  in  Concrete,  436. 
Shear  — 

in  Concrete-Steel  Beams,  405. 
Strength  in,  328. 
Tests  of,  90. 
Sheathing  for  Forms,  352. 

Tongue  and  Groove,  352. 
Shoefer  Kiln,  17. 


Short    Time    Tests,    Interpretation, 

137. 

Shrinkage  in  Setting,  331. 
Sidewalk,  Concrete,  420. 
Base,  421. 
Construction,  422. 
Cost,  425. 
Drainage,  420,  422. 
Foundation,  421. 
Wearing  Surface,  422. 
Sieves  for  Cement,  46,  51. 

Value  of  Coarse,  63. 
Sifting  (see  also  Fineness). 

Mechanical  and  Hand,  49. 
Time  of,  50. 
Silica,  10. 
Silica  Cement  — 

Manufacture,  21. 
Use  in  Locks,  492. 
Skip  for  Placing  Concrete,  372. 
Slaked  Lime  with  Cement,  245,  280. 
Slag  Cement  — 
Definition,  7. 
Manufacture,  23. 
Slag  Sand,  159. 

Smith  Concrete  Mixer,  210.  216. 
Soap  and  Alum  Solutions,  344. 
Soundness,  76. 
Tests  for  — 

A.  S.  C.  K.,  76. 
Boiling,  77. 
Chloride  Calcium,  81. 
Deval,  79. 
Discussion,  82. 
Faija,  78. 

German  Normal,  77. 
Hot,  for  Natural,  87. 
Hot  Water,  78. 
Kiln,  77. 
Le  Chatelier,  81. 
Records  of,  151. 
Warm  Water,  78. 
Spandrels,  Arch,  476. 
Special  Test  Records,  153. 
Specific  Gravity  Cement,  39. 
Effect  Aeration,  42. 

Coarse  Particles,  52. 


506 


INDEX 


Specifications     for    Concrete    Work, 

467. 

Specimens,  Marking,  146. 
Steel  Beams,  Concrete  Covered,  412. 
Steel  Facing  for  Curbs,  432. 
Forms  for  Sewers,  442. 
Lining  for  Forms,  353. 
Shell  for  Bridge  Piers,  465. 
Steel  with  Concrete,  387. 
Steinbriich  Mortar  Mixer,  107. 
Steps  in  Concrete  Construction,  362. 
Stone,  Broken  (see  Aggregate)  — 

vs.  Gravel,  192. 

Character  Surface  of,  276. 

Crushers,  194. 

Crushing,  195. 

Facing  for  Concrete,  477. 

Finish  for  Concrete,  367. 
Stop  Planks,  362. 
Storage  for  Cement,  144. 
Storing  Briquets,  117. 

before  Immersion,  117. 

in  Air,  122,  232,  246,  260. 

in  Sand,  123,  278. 

in  Water,  119. 
Storing    Concrete    Cubes,    Effect    of 

Medium,  293. 

Street  Railway  Foundations,  433. 
Strength    (see    Tensile,    Transverse, 
etc.). 

Compressive,  of  Concrete,  291. 
Mortar,  288. 

of  Concrete-Steel,  390,  403.  - 

Tensile,  of  Mortar,  227. 

Transverse,  of  Concrete,  313. 
Stringers  for  Street  Rails,  433. 
Subways,  Concrete,  443. 

Boston,  444,  446. 

Chicago  Telephone,  444. 

New  York,  443,  448. 
Sugar,  Effect  on  Time  Setting,  71. 
Sulphuric  Acid,  34,  368. 
Summary  of  Tests,  Record,  147. 
Surface  Concrete  (see  Finish). 
Surface  Stone,   Effect  on  Adhesion, 

276. 
Sylvester's  Process,  344. 


Tamping  Concrete,  359. 
Temperature  Cement  and  Water  — 

Effect  on  Tensile  Strength,  103. 

Time  Setting,  72. 
Temperature,  Low  — 

Use  of  Concrete  in,  326. 

Mortar  in,  260. 
Tensile    and    Compressive    Strength 

Compared,  288,  313. 
Tensile  Strength  — 

Effect  Sand,  227. 

Neglect  of,  in  Concrete-Steel,  388. 
Tensile  Tests  Cohesion,  95. 
Terra  Cotta,  Adhesion  of  Cement  to, 

274. 

Dust  with  Cement,  260. 
Test  Monier  Arch,  382. 
Testing  Machine,  Tensile,  123. 
Testing,  Uniform  Methods,  30. 
Tests   (see  also  Tensile,   Transverse, 
etc.)  - 

Abrasion,  94,  329. 

Adhesion,  92,  270. 

Chemical,  31. 

Cohesion,  95. 

Compression,  89,  288. 

Concrete,  291,  314. 

Fineness,  45. 

Sand,  96,  155. 

Shear,  90. 

Soundness,  76. 

Specific  Gravity,  39. 

Tensile,  95. 

Time  Setting,  65. 

Transverse,  90. 

Weight  per  Cubic  Foot,  37. 
Tetmajer,  Boiling  Test,  77. 

Kiln  Test,  77. 
Thacher  System,  385. 
Theory  of  Concrete-Steel  Beams,  387, 
390,  403. 

of  Proportions  in  Concrete,  200. 
Thermal  Expansion  Cement,  332. 
Tile,  Pulverized,  Use  of,  260. 
Time  Required  to  Sift,  49. 
Time  Setting  (see  Setting,  Rate  of). 
Tooling  Concrete  Surface,  367. 


INDEX 


507 


Top  Dressing,  Concrete  Walks,  422, 

424. 

Topeka  Bridge,  483. 
Transporting  Concrete,  358. 
Transverse  Strength  — 

Comparison  with  Tensile,  313. 

Concrete,  314. 

Mortar,  313. 

Tests  of  Cement,  90. 
Tremie  for  Placing  Concrete,  371. 
Trussed  Posts,  356. 
Wales,  357. 
Tube  Mill,  20. 
Tunnel  Lining  — - 

Brick  vs.  Concrete,  449. 

Cost,  452. 

Forms  for,  447. 

in  Firm  Earth,  444. 

in  Rock,  447. 

in  Soft  Ground,  446. 
Tunnels  — 

Aspen,  450. 

Cascades,  449. 

East  Boston,  446. 

Perkasie,  450. 

Sudbury  River  Aqueduct,  451. 
Twisted  Rods  — 

Adhesion  to,  284. 

Ransome,  386. 

Uniformity  in  Methods  Testing,  30. 

Viaduct,  Concrete-Steel,  484. 
Vicat  Needle  for  Time  Setting,  66. 
Voids  in  Aggregate,  190,  201. 
Voids  in  Sand,  162. 

Effect  Moisture,  166. 


Voids  in  Sand  — 

Effect  Shape  Grains,  162. 

Size  Grains,  163. 
Volume,  Proportions  by,  173,  200. 

Changes  in,  During  Setting, 
331. 

Wales,  Trussed,  357. 

Walks  of  Concrete^  420. 

Wall  Molds,  Buildings,  417. 
Parrel's,  417. 

Warehouse  for  Cement,  144. 

Washes  for  Concrete  Walls,  344. 

Washing  Sand,  169. 

Water  in   Mortar  and  Concrete   (see 
Consistency). 

Water,  Deposition  Concrete  in,  326, 
369. 

Water   of   Immersion    for    Briquets, 
119. 

Water,  Stale,  for  Immersing,  121. 

Waterproof     Construction     in    Sub- 
ways, 443. 

Waterproof    Mortar    and    Concrete, 
340,  343. 

Waterproof  Work  in  Reservoirs,  453. 

Wearing  Surface  of  Walks,  422. 

Wedge  Rammers  for  Concrete,  492. 

Weight  of  Concrete,  299,  305. 

Weight  per  Cubic  Foot  Cement,  37. 

Wells  in  Concrete,  362,  490. 

Wheelbarrows    for   Conveying    Con- 
crete, 359. 

White  Finish  for  Concrete,  365. 

Wire  in  Sieves,  47. 

Wires  for  Testing  Time  of  Setting,  66. 

Wunsch  System,  383. 


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